Polymeric nanoparticles useful in theranostics

ABSTRACT

Synthesis and characterization of starch based pH-responsive nanoparticles for controlled drug delivery are described. Polymethacrylic acid grafted starch (PMAA-g-St) nanoparticles with various molar ratio of starch to MAA were synthesized by a new one-pot method that enabled simultaneous grafting of PMAA and nanoparticle formation in an aqueous medium. NMR data showed that polysorbate 80 was polymerized into the graft polymer. Nanoparticles were relatively spherical with narrow size distribution and porous surface morphology and exhibited pH-dependent swelling in physiological pH range. The particle size and magnitude of volume phase transition were dependent on PMAA content and formulation parameters such as surfactant levels, cross-linker amount, and total monomer concentration. The results showed that the new pH-responsive nanoparticles possessed useful properties for controlled drug delivery.

FIELD OF THE INVENTION

The present invention relates to polymeric nanoparticles useful fordelivery of therapeutic and/or diagnostic agents.

BACKGROUND OF THE INVENTION

Many natural polysaccharides, such as starch and alginate, are found infood or used as food ingredients. Starch is one of the most abundantpolysaccharides occurring in nature. This biopolymer has a molecularformula of (C₆H₁₀O₅)_(n), with n ranging from 300 to 1000 [1]. Starch iscomposed of a mixture of two polymers called amylose and amylopectin [1,2]. Amylose molecules consists of α-D-glucopyranose units joined byα-1,4 acetal linkages. Amylopectin molecules are much larger and highlybranched. The molecule contains α-1,4 linear bounds, and is branchedthrough α-1,6 linkages [1, 2]. Most starches used in industry usuallycontain between 20 and 30% amylose with the remainder being amylopectin(70-80%) and minor components (less than 1%) such as lipids and protein[3].

Starch offers distinct advantages. Starch is relatively safe, havingbiocompatibility and biodegradability profiles well suited for in vivoapplications. In the context of colloidal systems, starch hasstabilizing properties making it a useful candidate for biomoleculardevelopment. Starch contains an abundance of hydroxyl groups capable ofundergoing various chemical reactions characteristic of alcohols. Thismakes it possible for a variety of drugs, targeting moieties, metalchelators, fluorescence probes, etc. to be conjugated to starch-basedmaterials. Starch-based materials can also be quite cost effective.Despite these advantages, starch has had limited use as a biomaterialand in drug delivery applications. Native starch has limited use due toits poor mechanical and chemical properties; however, variousmodifications can be made to improve the properties of starch andbroaden its applications. The most common chemical modifications aregrafting, oxidation, esterification, etherification, and hydrolysis. Thegrafting of starch with acrylic-based monomers can produce materialswith potential drug delivery and biomedical applications due to thecombination of biodegradable and stabilizing properties of starch withpH-responsive characteristics of acrylic polymer.

Starch-xanthan gum hydrogels have been synthesized for controlled drugdelivery by cross-linking starch and xanthan gum by sodiumtrimethaphosphate [4]. Starch has been modified by graftingpolymerization of various vinyl monomers [5] using radiation,photolysis, or catalysts and initiators such as metallic ions,peroxides, or persulfate [5-12]. Grafting of vinyl monomers onto starchis generally achieved by free radical initiation. Starch graftcopolymers have been used as hydrogels, flocculants, ion exchangers,superabsorbents, and so on [13-18].

Hydrophilic acrylic monomers can form hydrogels with adjustable swellingkinetics and have been utilized for drug delivery and other biomedicalapplications such as improvement of osteoblast adhesion [19-21].Combination of biodegradable properties of starch with pH responsivecharacteristics of acrylic based polymers may lead to interestinghydrogels with potentials in biomedical and drug delivery. Previouslypublished work has shown that potassium persulfate is able to initiategrafting of methacrylic acid onto starch; however, substantial amount ofhomopolymer is formed [22]. By using potassium persulfate/sodiumthiosulfate redox initiation system, Hebeish et al. were able toefficiently graft polymethacrylic acid onto starch while minimizinghomopolymer formation [6, 7].

In many applications, fast phase transition in response to environmentalstimuli, such as pH, is desirable. However, bulk hydrogels of largedimensions normally undergo slow dimensional change becauseconformational changes in polymeric networks and diffusion of solute andwater through the network take time. Since the response time isproportional to the square of diffusion distance, the phase transitionrate can be controlled by adjusting hydrogel dimensions [23]. Generally,nano-sized polymers undergo swelling equilibrium, and phase transitionin order of micro-seconds. Hence, stimulus responsive nanoparticles canbe potentially useful in stimulus-responsive drug delivery, and canserve as sensors or microswitches because of their extremely fastresponse to stimuli.

Despite numerous publications on grafting polymerization of vinylmonomers, the published data on development and characterization ofnano-sized starch based pH sensitive particles is very limited.Saboktakin et al. have recently described the grafting of thepolymethacrylic acid onto carboxymethyl starch to produce bulk polymer[24]. The authors have subsequently used a freeze drying method toproduce nanopowders; however, their method does not produce stablecolloidal dispersion of nanoparticles in aqueous medium. Saboktakin etal. have also described the grafting of the polymethacrylic acid ontochitosan nanoparticles as delivery systems for paclitaxel [24(a)].Hirosue et al. have described in international patent publication WO2010/084060 a polymer having a starch backbone onto which methylacrylatemonomer was grafted by atom transfer radical polymerization (ATRP)subsequent to modification of backbone hydroxyl groups by a linker suchas 2-bromo isobutyryl bromide. Nanoparticles were formulated with thestarch polymer by an emulsion diffusion method.

DESCRIPTION OF THE INVENTION

The invention described herein includes a method for the synthesis ofnanoparticles.

Nanoparticles of the invention include a polymer backbone having graftedthereto polymeric chains containing carboxyl groups or amino groups.Covalently linked as part of the nanoparticle are polyethoxylatemoieties that present on the exterior surface of the nanoparticles.

Nanoparticles of the invention are especially useful as carriers fore.g., therapeutics and/or signal molecules.

Preferably, nanoparticles of the invention are formed in aqueoussolution in a “one-pot” synthetic procedure in which a monomer graftpolymerizes onto a backbone polymer and polyethoxylate moietiesparticipate in the polymerization to become covalently incorporated aspart of the nanoparticle.

In disclosed embodiments, the polymer backbone is provided by starch,the monomer is methacrylic acid (MAA), diethylaminoethyl methacrylate(DEAEM), and the polyethoxylated moieties are provided by polysorbate 80(Tween® 80).

Nanoparticles of the invention are particularly useful as a carriernanoparticle. The cargo or payload of the carrier can be a therapeuticagent such as a drug, a signal molecule such as a fluorophore e.g.,fluoresceinamine, gadolinium, etc.

A therapeutic can be loaded to the nanoparticle after its formation.Alternatively, and especially where the particle cargo includes a signalor other molecule that is not intended to be dislodged from the carrierparticle while present in a patient, the polymer can be functionalizedwith the molecule by covalent attachment thereto before nanoparticleproduction. In disclosed examples, an organic chelator,diethylenetriaminepentaacetic dianhydride (DTPA bisanhydride), wascovalently linked to nanoparticles. In one example, DTPA was covalentlyattached to a polysaccharide polymer backbone prior to production of thenanoparticle; in another example, DTPA was linked to the already formednanoparticle. Gd⁺³ was loaded into the chelator preinstalled as part ofthe nanoparticle.

In another example, the drug doxorubicin hydrochloride, known to bewater soluble, was loaded into nanoparticles of the invention and invivo behaviour characterized.

It is possible to obtain nanoparticles of the invention having arelative low polydispersity index (PDI). An example of a monodispersioni.e., a composition in which the nanoparticles have a PDI of less than0.12 is provided.

Nanoparticles of the invention, in which multiple carboxyl groups oramino groups are present, are pH-sensitive, and examples illustratingphase transition in the order of milliseconds are provided. In oneaspect, the size of the exemplified particles as dependent upon variousprocessing parameters and pH, has been examined. Nanoparticlecompositions in which the average diameter varies from 100 nm to over300 nm are exemplified herein.

In the case of the anticancer drug doxorubicin, one example showsdrug-loaded nanoparticles providing an decrease in IC50 indrug-resistant cell lines, up to 19-fold decrease being observed. Apotential use of the carrier nanoparticles is thus in controlleddelivery of doxorubicin for the treatment of drug resistant breastcancer.

Gd⁺³-loaded nanoparticles can be used in magnetic resonance imaging(MRI) contrast agents, and this use is exemplified herein.

Use of nanoparticles having an organic fluorescent probe covalentlylinked to the particles is also exemplified with fluoresceinamine isomerI.

Nanoparticles of the invention have in vitro and in vivo applications.In vitro studies described herein, for example, indicate cellular uptakeof the particles by cancer cells and minimal cytotoxicity towardshepatocytes, suggesting useful for drug delivery and diagnosisapplications.

NMR studies of exemplified particles indicate that polysorbate 80 (PS80)is polymerized into the polymethacrylic acid grafted starchnanoparticles and present on the particle surface. Having thepolethoxylated polysorbate, which has been known to exhibit surfactantproperties, covalently bound to the nanoparticles provides stability tothe carrier in biological systems. Moreover, PS80 is known to bind lowdensity lipoprotein (LDL) in the blood facilitating nanoparticlecrossing the blood-brain barrier via LDL receptor-mediated transcytosis.The covalently bound PS80 may impart such particles with advantageousbrain targeting potential. Imaging data, in addition to our ex vivostudies described herein, provide evidence for the ability of thenanoparticles to cross blood brain barrier.

An embodiment of the invention is thus a method of producing ananoparticle, the method comprising the steps of:

-   -   (a) solubilising a polymer in a liquid solution;    -   (b) providing a polymerizable monomer comprising a carboxylic        acid side group;    -   (c) graft polymerizing the monomer to form polymeric chains on        the solubilised polymer,    -   (d) providing ethoxylated molecules having a functional group        reactive with the forming chains, wherein:        step (c) is conducted in the presence of the ethoxylated        molecules to covalently link the ethoxylated molecules to the        polymeric chains.

The liquid solution can include a hydroxylic solvent such as water, oneor more alcohols, particularly ethanol or a mixture of water andalcohol(s), particularly water and ethanol.

The polymer can be a polyhydroxyl polymer having a degree ofsubstitution between 0.05 and 3 per unit of the polymer, (or between 0.5and 3, or between 1 and 3, or between 2 and 3), the monomer can includean alkenyl group, and the graft polymerizing step can be conducted inthe presence of a cross-linking agent.

According to an embodiment, the monomer of step (c) is present in anamount between 1 and 20 times the amount of the cross-linking agent(mol/mol).

The step of polymerizing can be a free radical graft polymerizingprocess conducted in the presence of a free radical initiator. Theinitiator can be substantially free of transition metals. A particularinitiator is persulfate or functional equivalent thereof.

The ethoxylate groups of the ethoxylated molecules can terminate in freehydroxyl groups. The ethoxylated molecules can include an alkenyl groupwhich chemically reacts to covalently link the surfactant molecules tothe polymeric chains. In a particular embodiment, ethoxylated moleculesare a polyethoxylated sorbitan having a R(C9-C31)-C(O)O-group whereinthe sorbitan is linked to the second polymer through a C—C covalent bondof the R(C9-C31)-C(O)O-group during the step of polymerizing. TheR(C9-C31)-C(O)O-group can contain at least one C—C unsaturation whichreacts to form the C—C covalent bond in the step of polymerizing.

The amount of polymer and the amount of monomer of step (c) can beselected to produce a nanoparticle in which the molar ratio of monomericunits in the polymeric chains to monomeric units of the polymer isbetween 0.1 and 10.

The polymerizing step can be conducted in the presence of a surfactant,often an anionic surfactant.

Embodiments include producing a nanoparticle for delivery of abiological agent in which the agent is covalently linked to the polymerof step (a). The polymer can be a polyhydroxylated polymer in which theagent is covalently linked to the polymer by substitution of a hydroxylhydrogen atom thereof. The agent can be an organic moiety capable ofcomplexing a metal, and the method can include forming the metal-organicmoiety complex. The metal(s) can be selected to provide a signal inmagnetic resonance imaging e.g., can be Gd⁺³.

The amount of monomer of step (c) can be selected to be sufficientlyhigh such that the absolute value of the zeta potential, measured at pH7.4 and an ionic strength of 10 mM, of an aqueous solution of thenanoparticles produced is at least 15 mV.

Nanoparticles for delivery of a biological agent can be produced bydispersing the agent and nanoparticles obtained by a method of theinvention in a liquid medium to incorporate the agent into thenanoparticles.

Nanoparticles for delivery of a biological agent can be produced bycovalently linking to nanoparticles produced by a method of theinvention and the agent to carboxylic acid groups of the polymericchains of the nanoparticles.

According to an embodiment, the invention is a method of producing acarrier nanoparticle comprising the steps of:

-   -   (i) solubilising a polymer in an aqueous solution;    -   (ii) providing a polymerizable monomer comprising a carboxylic        acid side group;    -   (iii) graft polymerizing the monomer to form polymeric chains on        the solubilised polymer,    -   (iv) providing polyethoxylated molecules having a functional        group reactive with the forming chains, wherein:        polymerizing step (iii) is conducted in the presence of the        polyethoxylated molecules to covalently link the polyethoxylated        molecules to the forming chains and the polymerized product        forms into the nanoparticle with polyethoxylated moieties on the        exterior of the nanoparticle.

The invention includes a nanoparticle comprising: (a) a first polymer;(b) a second polymer grafted to the first polymer; and (c) apolyethoxylated moiety covalently bound to the second polymer.

In an embodiment, the second polymer of the nanoparticle can includepolymerized vinyl groups having about one carboxyl group per two carbonsof the backbone of the second polymer. The second polymer can be apolyalkenyl polymer. The polyalkenyl polymer can be a polyacrylic acid.According to a particular embodiment, the polyacrylic acid ispoly(methacrylic acid).

The polyethoxylated moiety can be a sorbitan having aR(C9-C31)-C(O)O-group wherein the sorbitan is linked to the secondpolymer through a C—C covalent bond of the R-group.

The first polymer of the nanoparticle can include a polyhydroxylpolymer.

The second polymer can be crosslinked.

Embodiments include a composition containing a plurality ofnanoparticles, composition can include a pharmaceutically active agent.Such an agent can be e.g., adsorbed to the nanoparticles.

A composition can include nanoparticles and a signal molecule. Thesignal molecule can be a metal chelated by an organic moiety, whereinthe moiety is covalently bound to the nanoparticles. An organic moietycan be covalently bound to the first polymer.

The signal molecule can be covalently bound to the nanoparticles,preferably covalently linked to a carboxylic acid side group. An exampleof a signal molecule is a fluorophore.

A composition containing nanoparticles can further include apharmaceutically active agent.

An embodiment includes a nanoparticle containing (I) a first polymercomprising a polysaccharide; (II) a second crosslinked polymercomprising poly(methacrylic acid) grafted to the first polymer; and(III) a polysorbate comprising a (C9-C31)R—C(O)O— group covalently boundto the second polymer by a C—C bond between the carbon backbone of thesecond polymer and the R group.

The (C9-C31)R—C(O)O-group of a nanoparticle can be —(C17)R—C(O)O— inwhich R is straight chain alkyl. The polysorbate can include the groups—O(CH₂CH₂O)_(w)—C(O)(C17)R, HO(CH₂CH₂O)_(x)—, —HO(CH₂CH₂O)_(y)—, and—HO(CH₂CH₂O)_(z)—, wherein w+x+y+z=20. The molecular weight of thepolysaccharide can be between about 2,600 and about 4,500 Da.

The molar ratio of the monomeric unit of the polysaccharide to themonomeric methacrylate units of the poly(methacrylic acid) can bebetween 0.2 and 8.0.

The molar ratio of the polysorbate and the monomeric methacrylate unitsof the poly(methacrylic acid) can be between 0.002 and 0.03.

An embodiment of the invention is method of producing a nanoparticlethat includes steps of:

-   -   (a) solubilising a polymer in a liquid solution;    -   (b) providing a polymerizable monomer comprising an        alkylaminoalkyl ester side group;    -   (c) providing a crosslinker; and    -   (d) graft polymerizing the monomer to form polymeric chains on        the solubilised polymer to form the nanoparticle.

The polymer can be a polyhydroxyl polymer having a degree ofsubstitution between 0.05 and 3 per unit of the polymer, the monomer caninclude an alkenyl group, and the graft polymerizing step can beconducted in the presence of a cross-linking agent. The polyhydroxylpolymer can have a degree of substitution between 1 and 3 per unit ofthe polymer.

The polymerizable monomer can be an alkylaminoalkyl ester of methacrylicacid e.g., diethylaminoethyl methacrylic acid.

The crosslinker can be ethylene glycol dimethacrylate.

The monomer of step (d) can be present in an amount of between 1 and 200times the amount of the cross-linking agent (mol/mol).

The amount of polymer and the amount of monomer of step (c) can beselected to produce a nanoparticle in which the molar ratio of monomericunits in the polymeric chains to monomeric units of the polymer isbetween 0.05 and 20 e.g., between 2 and 4.

A polysorbate can be present in step (d).

The polymerizable monomer can be present in an amount of between 5 and50 times the amount of the polysorbate (mol/mol), or between about 10and 40, or between about 15 and 35, or between about 20 and 30(mol/mol).

A non-ionic stabilizer e.g., polyvinylpyrollidone can be present in step(d).

The invention includes a nanoparticle containing (i) a first polymercomprising a polysaccharide; and (ii) a second crosslinked polymercomprising an alkylaminoalkyl ester of methacrylic acid grafted to thefirst polymer, wherein the second polymer is crosslinked.

The second polymer can be polymerized diethylaminoethyl methacrylicacid.

The second polymer can include polymerized vinyl groups having about onecarboxyl group per two carbons of the backbone of the second polymer.The polysaccharide can be a starch. The nanoparticles can be produced toexhibit an increased volume change of between 500 and 1500 fold when thepH of their ambient solution is changed from about 4 to about 7.4, orbetween about 600 and 1400, or between about 700 and about 1300 orbetween about 500 and about 1300 or between about 400 and 1100, orbetween about 700 and 1100, or about 800, or about 900, or about 1000,or about 1100 fold when the pH of their ambient solution is changed fromabout 4 to about 7.4.

BRIEF DESCRIPTION OF THE FIGURES AND TABLES

FIG. 1 shows graphical data for the interaction between doxorubicin andcarboxylic acid groups of nanoparticles having maximum stoichiometryof 1. (A) The blank differential enthalpy curves of titrating 8.5 mMdoxorubicin in buffers of various pH. (B) Differential enthalpy curvesof titrating 8.5 mM doxorubicin into 0.1 mg/ml PMAA-g-St-PS80nanoparticles in buffers of various pH. The ionic strength was keptconstant at 0.15 M by addition NaCl.

FIG. 2 shows FTIR spectra of (A) Starch, (B) PMAA-PS 80, and (C) PMAA-PS80-g-St. Major peaks are assigned and explained in the text.

FIG. 3 shows ¹H NMR spectra of A) PS 80, B) starch, C) PMAA-PS80, D)PMAA-PS80-g-St-2, E) PS80, F) starch, G) DTPA, H) St-DTPA, I) PMAA-PS80-g-St, and J) PMAA-PS 80-g-St-DTPA in 0.05M NaOD. Major peaks areassigned as indicated on the molecular schemes.

FIG. 4 shows PMAA-g-St-PS80-FITC extravasation from capillary lumencrossing the blood-brain barrier. Qualitative and quantitative resultsof brain distribution and accumulation for PMAA-PS 80-g-Stnanoparticles. Ex vivo near infrared fluorescence images of the wholebrain. (A) Ratio of the relative fluorescence intensity in brain as afunction of time after intravenous (iv) injection of nanoparticlescompared to normal brain not injected with nanoparticles. Data arepresented as means±standard deviation (n=4). (B) Fluorescence microscopyimages of perfused mouse brains 45 minutes following iv administrationof saline (left), PMAA-PS 80-g-St (middle) and PMAA-PS 80-g-St (right).The particles can be detected in the perivascular regions of the braincapillaries for samples treated with PMAA-PS 80-g-St nanoparticles.

FIG. 5 is a schematic illustrating the various steps in the reactionscheme of terpolymer synthesis.

FIG. 6 shows: (A) TEM images of PMAA-g-St-2 in 0.15 M PBS of pH=7.4. Thenanoparticles were stained with ammonium molybdate and dried-oncarbon-coated grid. (B) Intensity-weighted hydrodynamic diameter of thenanoparticles in 0.15 M pH 7.4 PBS. The particles showed a Gaussiandistribution and were relatively monodispersed.

FIG. 7 shows TEM images of PDEAEM-g-St-2 nanoparticles.

FIG. 8 shows: (A) relative diameter vs. pH for the nanoparticles withdifferent feed molar ratio of MAA/St in 0.15 M PBS. D_(7.4) and D₄ areparticles diameter at pH 7.4 and 4 respectively. (B) Effect of pH onsurface charge for particles of various MAA/St molar ratio.

The ionic strength was kept constant at 10 mM using NaCl. Data pointsrepresent the mean±standard deviation of three independent measurements.

FIG. 9 shows: (A) potentiometric titration curves. Empty trianglesrepresent the uncorrected potentiometric titration curve for PMAA-g-St-2latex dispersion. Solid content=0.104 wt %, C_(s)=0.05N NaCl, [NaOH]=0.1N, [HCl]=0.1N. Filled circles represent the titration curve aftercorrection. Empty circles show the blank titration curve. The arrowrepresents the equivalence point. The equivalence points are used tocalculate the MAA contents in various nanoparticle batches. (B)Variation in the apparent dissociation constant (pK_(a)) as a functionof the degree of ionization (α) for nanoparticles of different starchand MAA contents.

FIG. 10 shows forward and backward potentiometric titrations usingstabilization time of 30 s between injections. (A) PMAA, (B)PMAA-g-St-2, (C) PMAA-g-St-4. A lag time between forward and backwardtitrations was observed only in case of nanoparticles with high starchcontent.

FIG. 11 shows variation in the apparent dissociation constant (pK_(a))as a function of the degree of ionization (α) for nanoparticles ofvarious starch and MAA contents.

FIG. 12 shows effects of (A) SDS, (B) PS 80, (C) total monomerconcentration, and (D) cross-linker molar ratio on particle size and pHsensitivity. Filled squares represent particle size and filled trianglesrepresent relative particles diameter. Data points represent themean±standard deviation of three independent measurements.

FIG. 13 shows (A) number-weighted Gaussian distribution of PMAA-PS80-g-St nanoparticles loaded with doxorubicin (LC=33%) in 0.15 Mphosphate buffer at pH 7.4, and (B) transmission electron micrograph(TEM) of doxorubicin-loaded nanoparticles (LC=33%).

FIG. 14 shows XRD spectrum of (A) doxorubicin in native form, (B)PMAA-PS 80-g-St nanoparticles, (C) doxorubicin-loaded nanoparticles(LC=50%), and (D) doxorubicin-loaded nanoparticles (LC=50%) after 6months storage at room temperature. For doxorubicin clear peaks arevisible in the diffractogram indicating the presence of crystallinephase in the native form whereas nanoparticles show a typical amorphouspattern. Absence of peaks in the diffractograms of doxorubicin-loadednanoparticles indicates the phase transformation of crystallinedoxorubicin to amorphous doxorubicin.

FIG. 15 shows graphical data for the interaction between doxorubicin andcarboxylic acid groups of nanoparticles having maximum stoichiometryof 1. (A) The blank differential enthalpy curves of titrating 8.5 mMdoxorubicin in DDIW with various NaCl content. (B) Differential enthalpycurves of titrating 8.5 mM doxorubicin into 0.1 mg/ml PMAAg-St-PS80nanoparticles in DDIW with various NaCl content of various pH.

FIG. 16 shows pH-dependent doxorubicin release from the nanoparticles.The effects of pH on kinetics of doxorubicin release from thenanoparticles having a drug loading content of 50% at 37° C. areindicated. The release of free doxorubicin from the dialysis bag wasused as control. For each buffer system, the ionic strength was keptconstant at 0.15 M by adding NaCl.

FIG. 17 shows (A) fluorescence microscopy images of MDA-MB435/LCC6 cells(both wild-type (WT) and multidrug resistant (MDR1) with and without(control) 4 hr incubation with fluorescent NPs. Nuclei were stained withHoescht 33342 and visualized with DAPI filters, cell membranes werestained with Vybrant™DiI and visualized with Cy3 filters, and NPs werelabelled with fluoresceinamine isomer I and visualized with FITCfilters. Optical slices were taken every 2 μm from the uppermost andlowermost regions of the cell, allowing for selection of an image atapproximately the midpoint of the nucleus. (B) TEM micrographs ofMDA-MB435/LCC6 cells treated with 0.25 mg/ml PMAA-PS 80-g-St NPs for 4hrs. The nanoparticles were loaded with gadolinium ions (metal) andappear as electron dense deposits. Area indicated by dotted line inimage on the left is magnified in the image on the right.

FIG. 18 shows the nanoparticles are effectively endocytosed by wild-typeand drug-resistant human breast cancer cells. Flow cytometry histogramsfor MDA-MB435/LCC6 cells indicate the effect of incubation time andtemperature on particle uptake. The cells were incubated withfluorescently labelled nanoparticles at the final nanoparticleconcentration of 0.25 mg/ml at 37° C. (A) MDA-MB435/WT (1) background,(2) 1 hr incubation, (3) 4 hrs incubation, (4) 24 hrs incubation. (B)MDA-MB435/WT (1) background, (2) 4° C., (3) 24° C. (C) MDA-MB 435/MDR1(1) background, (2) 1 hr incubation, (3) 4 hrs incubation, (4) 24 hrsincubation. (D) MDA-MB435/MDR1 (1) background, (2) 4° C., (3) 24° C.Excitation using 488 nm argon ion laser and emission monitored at 530nm.

FIG. 19 illustrates doxorubicin-loaded nanoparticles exhibitsignificantly lower IC50 values in MDR1-expressing human breast cancercells. The response of MDA-MB435/LCC6 cell types to free doxorubicin anddoxorubicin-loaded nanoparticles by MTT assay was determined. (A-B) Cellviability of MDA-MB435/LCC6/WT (n=3) cells after exposure to increasingconcentrations of free doxorubicin and doxorubicin loaded nanoparticlesfor 24 hrs (A) and 48 hours (B). (C-D) Cell viability ofMDA435/LCC6/MDR1 (n=3) cells after exposure to increasing concentrationsof free doxorubicin and drug loaded nanoparticles for 24 hrs (C) and 48hrs (D). Cells with no treatment and incubated with blank nanoparticleswere used as control for free drug and drug loaded nanoparticlerespectively. Cell viability is expressed as the percent of control foreach treatment group. Data points represent the mean±standard deviationof the number of trials indicated for each experiment.

FIG. 20 shows (A) TEM images of SA-NPs and PF-NPs. (B) Dye-conjugatednanoparticles show NIR fluorescence characteristics. (C) Summary ofphysicochemical properties of SA-NPs and PF-NPs. Particle diameterrefers to the number-weighted diameter of readings averaged over 5minutes. Loading efficiency (LE %) is the fraction of originally addeddrug that was incorporated into the NPs, whereas drug loading content(LC %) is the percent of drug weight to total weight of thenanoparticles. All values are described as the mean±standard deviationof three independent trials. Total amount of Dox in the loading solutionwas 1.25 mg.

FIG. 21 shows coronal T₁-weighted (3D-FLASH, TE/TR 3/25 msec, flip angle20°) whole body images of Balb/c mice injected with (A) Omniscan® (0.1mmol/kg Gd³⁺), (B) PolyGd (0.025 mmol/kg Gd³⁺), and (C) PolyGd-Dox(0.025 mmol/Kg Gd³⁺). Heart, liver, bladder are represented in Slice A.Slice B shows kidneys, and vena cava. At one-fourth the dose ofOmniscan®, PolyGd and PolyGd-Dox produce much higher contrast over anextended period of time.

FIG. 22 shows the ratio of fluorescent intensity (normalized againstbaseline) for brain (left) and blood (right); the data provide evidencefor the deposition of the PMAA-g-St-PS80 in the brain.

FIG. 23 shows (A) TEM images of SA-NPs and PF-NPs. (B) Summary ofphysicochemical properties of SA-NPs and PF-NPs. Particle diameterrefers to the number-weighted diameter of readings averaged over 5minutes. Loading efficiency (LE %) is the fraction of originally addeddrug that was incorporated into the NPs, whereas drug loading content(LC %) is the percent of drug weight to total weight of thenanoparticles. All values are described as the mean±standard deviationof three independent trials. Total amount of Dox in the loading solutionwas 1.25 mg.

FIG. 24 shows (A) in vitro cytotoxicity of blank linear polymer andnanoparticles, Gd³⁺ loaded polymer and nanoparticles, and free Gd³⁺ inrat hepatocytes using trypan blue exclusion assay. Loading of Gd³⁺ intothe linear polymer and nanoparticle significantly reduced the Gd³⁺toxicity in the cells (* statistically significant compared to control(p<0.05)). (B) The toxicity of saline (black), blank polymer (darkgray), PolyGd (light gray) and free Gd³⁺ (white) to rat hepatocytes inculture exposed for 30 min, 60 min, 120 min, or 240 min. “% live”represents the percent of hepatocytes excluding trypan blue. The meansand standard deviations of three trials are shown. An asterisk (*)denotes a significant difference (p<0.05) in survival values compared tothe control.

FIG. 25 shows the toxicity of saline (black), blank polymer (dark gray),PolyGd (light gray) and free Gd³⁺ (white) to rat hepatocytes in cultureexposed for 30 min, 60 min, 120 min, or 240 min. “% live” represents thepercent of hepatocytes excluding trypan blue. The means and standarddeviations of three trials are shown. An asterisk (*) denotes asignificant difference (p<0.05) in survival values compared to thecontrol.

FIG. 26 shows (A) whole animal real time biodistribution and tumortargeting of SA-NPs and PF-NPs in mice bearing an orthotopic breasttumor model. Nanoparticle-associated fluorescence was determined priorto intravenous injection (baseline), and then at various hours followingnanoparticles injection up to 14 days. Tumor is indicated with an arrow.(B) Time-dependent excretion profiles of SA-NPs and PF-NPs from thewhole body (left) and tumor (right). The fluorescence intensity for theregion of interest was recorded as average radiant efficiency. Data arepresented as means±standard deviation (n=2×3). C)

FIG. 27 shows quantitative MRI of whole-body distribution: (A) R₁ mapsof Balb/c mice injected with Gd³⁺ loaded PMAA-g-St polymer (0.025mmol/kg Gd⁺³). (B) Change in relaxation rates, ΔR₁, of left ventricularblood, liver, bladder, and kidneys for Omniscan® (0.1 mmol/Kg Gd³⁺),PolyGd (0.025 mmol/Kg Gd³), and PolyGd-Dox (0.025 mmol/Kg Gd³⁺) overtime relative to baseline. PolyGd and PolyGd-Dox cause a much higherincrease in blood relaxation rate for an extended period of timecompared to Omniscan®. The data are presented as mean±standard deviationof three independent runs. (C) Quantitative results of tissuedistribution and tumor accumulation for SA-NPs and PF-NPs. Ratio of therelative fluorescence intensity in major organs, tumor, and blood as afunction of time after intravenous injection of nanoparticles, comparedto normal major organs and tumors not injected with NIR dyeconjugated-nanoparticles. Data are presented as means±standard deviation(n=2×3).

FIG. 28 shows quantitative results of tissue distribution and tumoraccumulation for SA-NPs and PF-NPs. Ratio of the relative fluorescenceintensity in major organs, tumor, and blood as a function of time afterintravenous injection of nanoparticles, compared to normal major organsand tumors not injected with NIR dye conjugated-nanoparticles. Data arepresented as means±standard deviation (n=2×3).

FIG. 29 shows biodistribution, elimination and tumor accumulation of thePolyGd (0.025 mmol/kg Gd³⁺) in tumor-bearing Balb/c mice. The Gd³⁺content was determined using ICP-AES. The data are presented asmeans±standard deviations of three independent runs.

FIG. 30 is a schematic of polysorbate 80 (PS80) incorporated into ananoparticle. PS80 is capable of binding to Apo-E which in turn binds toLDL receptors in brain microvessels, enabling transcytosis of thenanoparticle. NMR data indicate PS80 polymerization into the St-g-PMAAnanoparticles and linear polymers. Covalently bound PS80 ensuresstability in vivo.

FIG. 31 shows TOF-SIMS data indicating polysorbate 80 expression on theparticle surface. TOF-SIMS clearly shows the presence of PS80 by thecharacteristic peaks at 255, 265, 267, 281 and 283 in the positive ionmode representing the series of oleic, and stearic fatty acids that areside chains of the sorbitan molecule.

FIG. 32 shows MR imaging of the mouse brain following administration ofGd3+-loaded nanoparticles. (A) R₁ maps of the mice coronal brain slicesat baseline and 20 minutes after administration of PMAA-g-St-P80. (B)Brain R₁ values at various time points. (C) Quantitative MRI of braindistribution: R₁ maps of Balb/c mice (n=3) injected with Gd³⁺ loadedPMAA-PS 80-g-St nanoparticles (0.05 mmol/kg Gd⁺³). (D) Longitudinalrelaxation rates (R₁) of sagittal sinus, ventricles, cortex, andsub-cortex for Gd³⁺ loaded PMAA-PS 80-g-St-DTPA polymer overtime. Theasterisk (*) denotes a significant difference (p<0.05) in R₁ valuescompared to baseline. (E) Brain R₁ values at various time points.

FIG. 33 shows (A) Representative images of brain tumor acquired bybioluminescence imaging (left) and distribution of PMAA-PS 80-g-Stnanoparticles labeled with a near infrared dye (Hilyte Fluor 750,fluoresceinamine isomer I) (right). The results strongly suggest theaccumulation of the nanoparticles in the brain tumor. The brainmetastasis of

MDA-MB-231-luc-D3H2LN was established by intracranial injection of thecells. After a week, the brain tumor was imaged 3-5 min following i.p.injection of luciferin solution. The fluorescence image was acquired 6hours after tail vein injection of the nanoparticles. (B) Fluorescencemicroscopic image of a brain tumor section acquired using a DAPI and RFPfilter set to visualize the Hoescht 33342-stained cell nuclei (blue) andNIR HF 750-labeled nanoparticles. The image shows clearly thenanoparticles (red) and Dox (green) are colocalized suggesting the Doxdelivered by the nanoparticle to the tumor tissue and released from thenanoparticles in the brain tumor.

FIG. 34 shows Gd(III)-loaded linear polymers achieve significant MRcontrast in a mouse tumor model. (A) Tumor distribution of PolyGd(upper) and PolyGd-Dox (lower) (0.025 mmol/kg Gd³⁺): T₁-weighted images(1) and the corresponding R₁ maps (2). The arrows indicate the tumorimplanted subcutaneously in the right rear flank. (B) Time course of ΔR₁in tumor periphery and tumor core, displaying elevated tumor R₁ even 48hours after contrast agent injection. The data are presented asmean±standard deviation of three independent runs.

FIG. 35 shows anti-tumor activity of starch-based nanoparticles inEMT6/WT tumor bearing mice. Tumor cells were implanted orthotopically onday zero. Mice were treated with (A) 5% dextrose (n=2×4), (B) free Dox(n=8), PF-NPs (n=2×4), (C) PF-NPs, and (D) SA-NPs (n=2×3) at a dose of2×10 mg/kg equivalent to Dox on day 8 and 15. Tumor volume up to day 62.Each curve represents one animal. (E) Kaplan Meier survival curves for5% dextrose, free Dox, PF-NPs, and SA-NPs. The trend in survival curveswere significantly different (p=0.0033, Mantel Cox). The mice weretreated by intravenous injection of various formulations at day 8 andday 15. (F) Time profiles of body weight of tumor-bearing mice treatedwith 5% dextrose (n=2×4), free Dox (n=2×4), PF-NPs (n=2×4), and SA-NPs(n=2×3) at a dose of 2×10 mg/kg equivalent to Dox. Balb/c mice wereinoculated with EMT6/WT tumor in the mammary fat pad and receivedtreatment on day 8 and 15 post inoculation. Each curve represents oneanimal. (G) Time profiles of body weight of tumor-bearing mice treatedwith 5% dextrose (n=2×4), free Dox (n=2×4), PF-NPs (n=2×4), and SA-NPs(n=2×3) at a dose of 2×10 mg/kg equivalent to Dox. Balb/c mice wereinoculated with EMT6/WT tumor in the mammary fat pad and receivedtreatment on day 8 and 15 post inoculation. Each curve represents oneanimal.

FIG. 36 shows (A) MIP angiogram displaying contrast enhancement of (1)whole body and (2) neck and head regions, obtained prior to (baseline)and at 15 minutes following Gd³⁺ loaded PMAA-g-St-DTPA injection at 0.03mmol Gd/kg. (B) Kinetics of vascular signal to noise (S/N) ratio andcontrast to-noise (C/N) ratio measured from the inferior vena cava inwhole-body angiograms. * denotes a significant difference compared tobaseline (p<0.05). The data are presented as mean and standard deviationof three independent runs.

FIG. 37 shows FTIR spectra of (A) pure starch, (B) PDEAEM, and (C)PDEAEM-g-St.

FIG. 38 shows H NMR spectra of (A) starch, (B) PDEAEM, and (C)PDEAEM-g-St.

FIG. 39 shows intensity-weight distribution of PDEAEM-g-St-1nanoparticles in 0.15M PBS pH=4.

FIG. 40 shows intensity-weight distribution of PDEAEM-g-St-1 in 0.15 MPBS pH=7.4.

FIG. 41 shows diameter of the PDEAEM-g-St particles of various starchcomposition at 25° C. as a function of pH of the medium.

FIG. 42 shows diameter of Gd-conjugated PDEAEM-g-St-DTPA nanoparticlesat different pH.

FIG. 43 shows near infrared dye conjugation in the nanoparticles. A) Aschematic of the conjugation reaction. (B) The PMAA-g-St-PS80 labelledwith a NIR dye compared to blank. C) Nanoparticles show fluorescenceemission at 820 nm with dye content of 4.3 μmol/g.

FIG. 44 shows (A) tumor accumulation of the PMAA-g-St-P80 polymer inmurine breast cancer tumor model. The animal was imaged at differenttime points after tail vein injection of 0.2 ml of PMAA-g-St-PS80 (4.5mg/ml). The tumor is indicated with arrow.

Table 1 shows nanoparticle preparation recipes and polymer composition.Reaction yield was defined as the ratio of purified terpolymer to thetotal weight of MAA, PS 80, and starch in the feed.

Table 2 shows characterization of the drug-loaded nanoparticles. Theeffect of drug loading on the particle size and surface charge is shown.Particle diameter refers to the number-weighted diameter of readingsaveraged over 5 minutes. Loading efficiency is the fraction oforiginally added drug that was incorporated into the NPs, whereas drugloading content is the percent of drug weight to total weight of thenanoparticles. All values are reported as the mean±standard deviation ofthree independent trials.

Table 3 shows intensity-weighted hydrodynamic diameter of nanoparticleswith different feed molar ratio of MAA/St in 0.15 M PBS of various pH.The ionic strength was kept constant using NaCl. All values aredescribed as the mean±standard deviation of three independent trials.

Table 4 shows feed and product MAA contents calculated from titrationdata along with zeta potential values in buffers of pH 4 and pH 7.4 andionic strength of 10 mM. All values are described as the mean±standarddeviation of three independent trials.

Table 5A shows Gd⁺³ content and in vitro relaxivity ofSt-DTPA-g-PMAA-P80; the relaxivity was measured in 0.9% NaCl at 3T and7T. Omniscan has been included for comparison.

Table 5B shows Gd³⁺ content, Dox content, molecular weight, particlesize, and r₁ for Omniscan®, PolyGd, and PolyGd-Dox. The r₁ were measuredin saline at 3 and 7 T. Means and standard deviations of threeindependent experiments are shown. Molecular weight of Omniscan® wascalculated based on its molecular formula.

Table 6 shows Gd³⁺ content, Dox content, molecular weight, particlesize, and r₁ for Omniscan®, PolyGd, and PolyGd-Dox. The r₁ were measuredin saline at 3 and 7 T. Means and standard deviations of threeindependent experiments are shown. Molecular weight of Omniscan® wascalculated based on its molecular formula.

Table 7 shows feed composition of various PDEAEM-g-St batches.

EXAMPLES Chemical and Reagents

Soluble starch (MW 2,600-4,500 Da), methacrylic acid (MAA),N,N′-Methylenebisacrylamide (MBA) sodium thiosulfate (STS), potassiumpersulfate (KPS), polysorbate 80 (PS 80), and sodium dodecyl sulfate(SDS) were purchased from Sigma-Aldrich Canada (Oakville, ON, Canada).MAA inhibitor was removed by vacuum distillation prior to use. All otherchemicals were reagent grade and were used as received.

Cell Line and Maintenance

The murine breast carcinoma cell line EMT6/WT was initially provided byDr. Ian Tannock (Ontario Cancer Institute, Toronto, ON, Canada) and nowmaintained in our laboratory. Monolayers of cells were cultured on 75cm² polystyrene tissue culture flasks at 37° C. in 5% CO2/95% airhumidified incubator. Cancer cells were maintained in α-minimalessential medium (Ontario Cancer Institute Media Laboratory, Toronto,ON, Canada), supplemented with 10% fetal bovine serum (Cansera Inc.,Etobicoke, ON, Canada). Cells grown to confluence were trypsinized with0.05% trypsin-EDTA (Invitrogen Inc., Burlington, ON, Canada), diluted(1/10) in a fresh growth medium and reseeded.

Experimental Animals and Induction of Orthotopic Breast Tumors

All animal work was approved by the animal care committee at theUniversity Health Network, and all experiments were performed inaccordance with all guidelines and regulations put forth by the CanadianCouncil on Animal Care. 8 week old female Balb/c mice (Jacksonlaboratory, Maine, USA) were used. The animals were allowed free accessto food and water throughout the study. For tumor studies, 1 millionmurine EMT6 breast cancer cells were injected subcutaneously into theleft flank. Tumors were monitored for growth and MRI studies wereinitiated at tumor average diameter of 5 mm.

Preparation and Characterization of Nanoparticles Example 1 Synthesis ofPolymethacrylic Acid-Grafted-Starch (PMAA-g-St) Nanoparticles

Synthesis of PMAA-PS-80-g-St Nanoparticles

A free radical dispersion polymerization method was used to preparePMAA-g-St nanoparticles in one-pot using potassium persulfate/sodiumthiosulfate initiation (KPS/STS) system. A series of preliminary studieswere performed to identify suitable surfactants type and concentrationas well as monomer concentration required to obtain stable particles.

The polymerization was conducted in a 500 ml three-necked flask fittedwith nitrogen inlet, condenser, thermometer, and magnetic stirrer whichwas immersed in a water bath. The desired amount of starch was dissolvedin distilled water by heating at 95° C. for 30 minutes, cooled down to70° C., and purged with N₂ for 30 minutes to remove any dissolvedoxygen. Subsequently, desired amounts of SDS, PS 80, KPS and STS wereadded to the starch solution while under stirring. After 15 minutes, thereaction was started by adding required amounts of nitrogen purged MAAand MBA to the solution. Opalescence appeared after 5 minutes and thereaction was continued for 8 hours at 70° C. to ensure completeconversion. The product was washed extensively with warm water twice andextracted with methanol followed by ultracentrifugation to remove anyunreacted materials and homopolymers. The purified particles were freezedried and stored in a desiccator for future use.

The grafting yield percent (GY %) was calculated using equation 1:

$\begin{matrix}{{{GY}\mspace{14mu} \%} = {\frac{W_{I}}{W_{T}} \times 100\%}} & (1)\end{matrix}$

where W₁ is the weight of purified product and W_(T) is total weight ofmonomers in the feed.

In another example, the polymerization was conducted in a 500 mlthree-necked flask which was immersed in a water bath and equipped withnitrogen inlet, a condenser, a thermometer, and a magnetic stirrer.First, a desired amount of starch (FIG. 1) was dissolved in 170 ml ofdistilled deionized water (DDIW) which was heated at 95° C. for 30minutes. The solution was cooled down to 70° C., and purged with N₂ for30 minutes to remove any dissolved oxygen. Next, 0.45 mmol of KPS and1.36 mmol of STS dissolved in 5 ml of DDIW were added. After 10 minutes,desired amounts of SDS and PS 80 (FIG. 1) dissolved in 10 ml of DDIWwere added to the reaction mixture with stirring. After 15 minutes, thereaction was started by adding known amounts of MAA and MBA (Table 1) in10 ml of water purged by nitrogen, and the final solution volume wasadjusted to 200 ml by adding DDIW (Table 1). Opalescence appeared after5 minutes and the reaction was continued for 8 hours at 70° C. to ensurecomplete conversion. The product was washed extensively with warm waterand methanol followed by ultracentrifugation (96,000 g) to remove anyunreacted materials and homo-polymers. The purified particles werefreeze-dried and stored in a desiccator for future use.

The reaction yield percent (RY %) was calculated using the followingequation:

${{RY}\mspace{14mu} \%} = {\frac{W_{1}}{W_{T}} \times 100\%}$

where W₁ is the weight of purified product and W_(T) is total weight ofMAA, starch, and PS 80 in the feed.Confirmation of Grafting with Fourier Transform Infrared Spectroscopy(FTIR)

FTIR spectra were recorded on a Perkin Elmer Spectrum 1000 seriesspectrometer (MA, USA). Spectra were taken with a resolution of 4 cm⁻¹and averaged over 32 scans. Samples were thoroughly ground withexhaustively dried KBr and pellets were prepared by compression undervacuum.

Proton Nuclear Magnetic Resonance Spectroscopy (¹H NMR)

¹H NMR measurements were obtained using a Varian Mercury 400 MHz (CA,USA). The PMAA-g-St (with no cross-linking) samples were dissolved in0.01 M NaOD to obtain a solution concentration of 15 mg/ml. The spectrawere obtained with a pulse angle of 25°, a delay time of 10 s, and anacquisition time of 2 s. All chemical shifts are reported in parts permillion (ppm) with water peak as the reference.

Examination of the Nanoparticles with Transmission Electron Microscopy(TEM)

Transmission electron microscopy (TEM) was used to examine the shapesand morphologies of the nanoparticles. Nanoparticle suspensions in PBS(pH=7.4) were stained with ammonium molybdate and placed oncarbon-coated grids. The samples were blotted with filter paper and leftto dry. Transmission electron micrographs were acquired on a HitachiH7000 electron microscope (Hitachi Canada, Ltd., Mississauga, ON,Canada) with accelerating voltage of 100 kV.

Determination of Particle Size by Dynamic Light Scattering

In one example, particle size was measured by dynamic light scattering(DLS), using a NICOMP™ 380ZLS (PSSNICOMP, Santa Barbara, Calif., USA)apparatus. The particle size was measured at 37° C. with a HeNe laserbeam at a detection angle of 90°. The purified latexes were dispersed indistilled water to prepare a stock latex suspension of 5 mg/ml with theaid of Hielscher UP100H probe ultrasonicator (Hielscher USA, Inc.,Ringwood N.J., USA) at 80% peak amplitude and 5 mm probe depth insolution for 5 minutes. The stock suspension was diluted 10 times withthe aqueous buffer solutions of various pH and constant ionic strengthof 0.15M. The pH in the resultant dilute latex suspension was confirmedwith a pH meter. The particle size for each sample was measured threetimes and the average of the triplicate was reported. Theintensity-weighted mean diameter was used as the hydrodynamic size sinceit is calculated directly from the original data and more reproduciblethan volume-weighted and number-weighted mean diameter. The particlesize distribution was evaluated using polydispersity index (PdI).Generally, particles with PdI values smaller than 0.12 are consideredmonodisperse.

Zeta Potential Measurement

To study the effect of particle composition and pH on surface charge,particles zeta potential was measured using electrophoretic mobility.The stock latex suspension was diluted with buffer solutions ofdifferent pH and constant ionic strength of 10 mM. The zeta potentialwas then measured using a Malvern zeta sizer Nano-ZS (Malvern,Worcestershire, UK).

To measure electrophoretic mobility values of the nanoparticles, thestock latex suspension was diluted with buffer solutions of different pHand constant ionic strength of 10 mM. The measured electrophoreticmobility (μ) is related to the zeta potential (ξ) using the followingequation [25]:

$\xi = {\frac{3}{2}\left( \frac{\mu \; n}{ɛ_{0}ɛ_{r}{f\left( {\kappa \; R} \right)}} \right)}$

where R is the particle radius, η is the solution viscosity, κ is theinverse Debye length, ∈₀ is where R is the particle radius, η is thesolution viscosity, κ is the inverse Debye length, ∈₀, is thepermittivity of a vacuum, ∈_(r) is the medium dielectric constant, andƒ(κR) is Henry's function for a 1:1 electrolyte.

Titration Studies

Potentiometric titrations were carried out with a Fisher ScientificAccumet AB15 pH meter (Fisher Scientific, Toronto, ON, Canada). Sampleswere prepared by suspending 0.050 g of purified particles in 50 mL of0.05M NaCl. Titrations were run in a thoroughly cleaned,temperature-controlled (25° C.) 100 mL beaker fitted with a pH electrode(Fisher Scientific), and a nitrogen line. The polymer suspension wasstirred continuously using a magnetic stirrer. 0.1 M volumetric standardsolutions of HCl and NaOH (Fisher Scientific, Toronto, ON, Canada) wereused as titrants. The pH of the latex was lowered to 3.0, and nitrogenwas bubbled through the latex for 20 minutes prior to titration toremove dissolved carbon dioxide from the system. Nitrogen was blowngently on the sample during the titration to maintain an inertatmosphere. Unless otherwise noted, all data were acquired using aforward (base-into-acid) titration. The suspension was allowed tostabilize for 5 minutes between each titrant addition to ensureequilibrium. The original titration data was corrected by taking intothe account the contribution of free H⁺ and OH⁻, making the end pointclearer.

The correction is performed according to equation [26, 27]:

[V] _(pH) =[V _(NaOH)]_(pH) +[V _(H) ₊ ⁰]_(pH) −[V _(OH) ⁻ ⁰]_(pH)

where [V_(NaOH)] is the volume of NaOH added to the dispersion and[V_(H) ₊ ⁰] and [V_(OH) ⁻ ⁰] are the volumes of HCl and NaOH added to ablank solution of the same pH as in the dispersion. With thiscorrection, assuming the same activity coefficient for H⁺ and OH⁻ in thedispersion and in the blank solution, the value of [V]_(pH) should be aconstant at equivalence point.

PMAA-g-St Nanoparticles Synthesis

Stable PMAA-g-St latexes with solid contents of up to 7.2% were preparedusing the described method. The grafting was performed using a modifiedaqueous dispersion polymerization method enabling the simultaneousgrafting and nanoparticle formation in a one-pot synthesis procedure.The method was found not to require the use of oils and organicsolvents. Initially, monomers, surfactants, and initiators are allsoluble in water.

As depicted in Table 1, the reaction yield (RY %) increases withincreasing MAA concentration in the feed. This result may be explainedby greater availability of MAA molecules in the proximity of starch andPS 80 at higher MAA concentrations. The starch macroradicals are lessmobile than MAA and, thus, their reaction with MAA monomer wouldbasically depend on the availability of the monomer molecules in closevicinity.

Without being bound by any theory, it is thought that as the initiatorsdecompose at elevated temperature, the generated free radicals, onstarch, react with solute monomers to form oligomeric radicals. Growingoligomer chains associate with each other increasingly as theirmolecular weight and concentration rise. At a critical chain length, theformed grafted polymer becomes insoluble in low pH medium (due toprotonataion of carboxylic groups, and production of sulphate ions fromthe initiators) and adsorbs stabilizers to form stable particle nuclei.Once particles have been formed, they absorb monomer from the continuousphase. From this stage on, polymerization mainly takes place within themonomer-swollen particles.

Table 1 summarizes the recipes of selected nanoparticle batches, andtheir respective grafting yields (GY %). Increasing the MAAconcentration was accompanied by increase in the grafting yield. Thiscould be explained in terms of greater availability of monomer moleculesin the proximity of starch at higher MAA concentrations. The starchmacroradicals are relatively immobile. As a result, the reaction ofthese macromolecules with monomers would essentially depend on theavailability of MAA monomers on the starch vicinity.

The successful synthesis of the terpolymer nanoparticles by the newdispersion polymerization method may be explained as follows. Initially,all the reactants are soluble in water. As the polymerization proceeds,the formed terpolymer, at a critical chain length, becomes insoluble inthe polymerization medium of low pH due to protonation of carboxylicgroups and presence of PS 80 hydrophobic side chains. Moreover, PMAA isknown to exhibit lower critical solution temperature (LCST) of 50° C.,which means that it can precipitate from aqueous solutions at thepolymerization temperature of 70° C. [28-30]. The LCST properties ofPMAA may also contribute to the nanoparticle formation. The polymer“nano-precipitates” can adsorb stabilizers to form particle nuclei. Thenthey can absorb monomers or low molecular weight radicals from thecontinuous phase and grow larger. With the assistance of thesurfactants, the larger nanoparticles are stabilized. Based on the phasetransition properties of the formed terpolymer under the polymerizationcondition, we have developed this new aqueous dispersion polymerizationmethod which enables the simultaneous grafting and nanoparticleformation in a one-pot synthesis process. This method does not requireuse of oils and organic solvents and thus is advantageous over reversemicroemulsion polymerization method.

Mechanism of Grafting and Polymer Composition

FTIR and NMR studies were used to confirm grafting and study the polymercomposition and mechanism of grafting. The FTIR spectra of starch, PMAAand grafted starch are shown in FIG. 2. In comparison with the spectrumof the native starch, the major change is the presence of a carbonyl C═Oabsorption frequency at 1738 cm⁻¹. The peaks at 1166 cm⁻¹, 1090 cm⁻¹,1020 cm⁻¹, and 954 cm⁻¹ in native starch are due to the CO bondstretching. The peaks at 1090 cm⁻¹ and 1020 cm⁻¹ are characteristic ofthe anhydroglucose ring CO/CC stretching. A characteristic peak at 1645cm⁻¹ is due to the presence of bound water in starch. A broadband due tohydrogen bonded hydroxyl group (O—H) appears at 3450 cm⁻¹ and isattributed to the complex vibrational stretching, associated with free,inter and intra molecular bound hydroxyl groups. The band at 2940 cm⁻¹is characteristic of C—H stretching. The strong OH stretching band at3450 cm⁻¹ in the native starch decreases in intensity following thegrafting reaction implying the reaction of starch with MAA throughstarch OH groups. Also, the grafted polymer exhibits characteristicspeaks of pyranose ring vibrations at 520-920 cm⁻¹ and also CO/CC ringstretching at 1032 cm⁻¹ which is absent in MAA homopolymer confirmingthe grafting of PMAA onto starch.

FIG. 3 shows the ¹H-NMR spectra of a) PS 80, b) soluble starch, c) PMAAand d) PMAA-g-St. The peak at 0.86 ppm corresponds to aliphatic CH₃protons of the PS 80. The peak at 1.27 comes from the aliphatic CH₂region of the surfactant. The large peak at 3.62 ppm is from the CH₂protons of polyethylene oxide regions of the PS 80. The small peak at5.33 is from CH groups in fatty acid chain (double bond). The smallerpeaks in the aliphatic regions belong to the various moieties of fattyacid tails. The starch spectrum exhibits characteristic peaks at 3.5ppm, which was attributed to CH₂ of starch units linked to C6 carbons.The peak at 3.8 ppm is attributed to the hydrogens linked to the CHunits joined to C1-C5 carbons. The peak at 5.1 ppm is attributed to thehydrogens of the R—OH hydroxyl groups. Interestingly, the spectrum ofhomopolymer PMAA exhibits peaks characteristics of both PMAA and PS 80.The peaks at 0.94 ppm and 1.66 ppm are from CH₃ and CH₂ of the PMAArespectively. The CH peak at 5.33 ppm is absent in the PS 80-PMAAcopolymer indicating that PS 80 reacts with the MAA monomers through itsdouble bond. PS 80 contains mono-, di-, and tri-unsaturated fatty acidesters as the primary hydrophobic substituent, which raises thepossibility of polymerization pathway for this surfactant. Moreover, theability of PS 80 to participate in oxidative reactions has been welldocumented in the literature [31-33]. In fact, PS 80 has been used as anoxidizing reagent for the assessment of drug stability [34]. In thepresence of initiators, an alkyl free radical on the surfactant can beformed by hydrogen abstraction. This may occur by various processes,including thermal or photochemical homolytic cleavage of an RH bond.Subsequently, the free radical can participate in graft polymerizationreactions by attacking monomer double bond.

The ¹H NMR spectrum of PMAA-g-St polymer shows peaks characteristics ofstarch, MAA, and PS 80. There is a small shift in peaks at 0.94, 1.29,1.66, 3.5 as well as a slight change of shape in peak at 3.5 ppm due toalteration of chemical environment brought on by grafting. Also, thereis reduction in relative intensity of the peak at 5.1 indicating thatthe starch hydroxyl groups are participating in the grafting reaction.This peak depends linearly on the amount of anhydroglucose units presentin the sample. The areas under the peaks at 3.52, 3.70, and 1.66 wereused to calculate the molar ratio of starch, MMA, and PS 80 in the finalproduct and presented in Table 1. In addition, using the equivalentpoint data from the titration studies, we determined the MAA contents inthe nanoparticles prepared with different feed monomer ratios. Thesedata are also presented in Table 2. There is a relatively good relationbetween MAA and starch molar ratio in the feed and product. However,only a small fraction of the PS 80 in the feed is incorporated into thefinal product. The relative molar ratio of the surfactant in the finalproduct decreases as the amount of MAA in the feed is reduced perhapsimplying that PS 80 is mainly incorporated into the graft polymerthrough copolymerization with MAA monomers.

Additional FTIR and H¹ NMR spectra are presented in FIG. 4 Theinitiation process and free radical formation for grafting of PMAA ontostarch can be described by the following reaction schemes [35, 36]:

S₂O₈ ²⁻→2SO₄.⁻  (1)

2SO₄.⁻→end products  (2)

SO₄.⁻+S₂O₃ ⁻²→SO₄ ²⁻+S₂O₃.⁻  (3)

S₂O₃.⁻+S₂O₃ ⁻²+SO₄.⁻→SO₄ ²⁻+S₄O₆ ²⁻  (4)

SO₄.⁻+H₂O→HSO⁻ ₄+HO.  (5)

S₂O₃.⁻+H₂O→HS₂O₃ ⁻+HO.  (6)

St-H+HO.→St.+H₂O  (7)

St-H+S₂O₃.⁻→St.+HS₂O₃  (8)

St-H+SO₄.⁻→St.+HSO⁻ ₄  (9)

Reaction (3), (5), and (6) favor the continuous formation of variousfree radical species while reaction (2) and (4) lead to free radicaldisappearance. It is believed that in presence of thiosulfate there aredifferent free radicals: the sulfate, the thiosulfate, and the hydroxylradicals which can attack the starch resulting in hydrogen abstractionand the formation of free radicals on the starch molecules. The hydroxylradicals or starch radicals can attack the MAA double bond and inducethe grafting of MAA onto the starch. Thus, subsequent addition of MAAmolecules to the initiated chain propagates the grafting chain accordingto FIG. 5. Finally, the growing grafted chain is terminated bycombination or disproportion (FIG. 5). It has to be noted thatconcurrent homopolymerization of MAA still occurs to some degree due toinitiating action of free radicals on MAA monomers.

Morphology and Particle Size of Nanoparticles

All nanoparticles analyzed presented a very homogeneous morphology withparticle size around 100-200 nm and a rather spherical shape (FIG. 6A).The nanoparticles have a porous cotton ball like surface morphology.Having a porous structure might be beneficial in terms of faster phasetransition in response to environmental stimuli such as pH as well aspromoting higher drug loading. There is also some degree of particleaggregation and fusion present; however, this might be due to nature ofTEM sample preparation. Particles that are deposited in close proximityon the TEM grid can partly fuse together due to the influence of dryingand the electron beam. Such behavior is typical and has been frequentlyreported for other polymeric nanoparticles such poly(2-hydroxy ethylmethacrylate) particles [37].

As shown in Table 3, the particle sizes of the nanoparticles ranged from70 nm to 310 nm for the terpolymer PMAA-PS 80-g-St-3 depending on thepolymer composition and pH. A typical particle size distribution plotfrom DLS measurement is presented in FIG. 6B. In general, the particlesize distribution is relatively narrow with the polydispersity index PdIaround 0.09-0.14, except the PMAA nanoparticles (PdI=0.26). Particlesize is a crucial parameter in determining the nanoparticles performancein pharmaceutical applications. It affects properties such as responserate (to stimuli such as pH), drug release, cellular uptake as well asparticles ability to effectively kill cancer cells. In addition,particle size greatly influences in vivo pharmacokinetics andbiodistribution and thus the therapeutic effects of the encapsulateddrugs. The particle size of PMAA-g-St nanoparticles makes them amenableto cellular uptake mechanisms, as well as to the enhanced permeabilityand retention (EPR) effect that imparts passive tumor targetingproperties on the nanoparticles [38]. Due to the porosity of the tumorvasculature (the effective mean pore size of most peripheral humantumors is about 300 nm) and the lack of lymphatic drainage, colloidalnanoparticles of suitable size are preferentially distributed in thetumors by the EPR.

The TEM photographs (FIG. 6) of a typical sample illustrate that thenanoparticles have particle size around 100-200 nm, a nearly sphericalshape, and porous, cotton ball-like morphology. A porous structure mightbe beneficial in terms of faster phase transition in response toenvironmental stimuli such as pH as well as promoting higher drugloading than a dense structure. FIG. 7 shows TEM images of PDEAEM-g-St-2nanoparticles.

A uniform particle size is also important for drug delivery applicationsbecause the distribution of the nanoparticles in the body and theirinteraction with biological cells are greatly affected by the particlesize. Generally, the monodisperse particles exhibit more uniformphysical and chemical properties making it easier to formulate moresophisticated intelligent drug delivery systems.

PMAA-g-St Nanoparticles Show pH-Responsive Swelling in Physiological pHRange

The results in Table 3 and FIG. 8A demonstrate that the particle sizeincreases with increasing pH from 5 to 7.4 and the pH-dependent changein particle size is a function of MAA/St molar ratio. FIG. 8demonstrates that the particle size increases with increasing pH from 4to 7.4 and the magnitude of the increase is determined by the MAAcontent. For example, the average diameter of PMAA nanoparticlesincreases 2.2 times from 70.5 nm at pH 4 to 152 nm at pH 7.4, while thatPMAA-g-St-4 only increases 1.2 fold, translating to a volume ratio(V₇₄N₄) of 10.1 for PMAA and 1.5 for PMAA-g-St-4. In general, theincrease in starch content resulted in reduction in pH sensitivity. Thiscan be ascribed to the fact that lower MAA content results in smallerelectrostatic repulsion attributed to the lower content of ionizedcarboxylic groups and thus lower swelling. Different pH sensitivitymeans a different amount of ionizable and/or ionized carboxylic groups.A lower MAA content results in smaller electrostatic repulsion and lowerswelling at pH 7.4, leading to a smaller V_(7.4)/V₄ value.

FIG. 8A also shows that a dramatic increase in particle diameter occursbetween pH 5 and pH 6, indicating ionization transition in this region,consistent with the volume phase transition pH of PMAA-containingnanoparticles [39]. At pH values lower than the pKa of PMAA, theprotonated carboxylic acid groups form extensive hydrogen bondingleading to a collapsed structure. At higher pH values, increasedionization of the carboxylic acid groups results in high electrostaticrepulsive forces between polymer chains and thus enlarged the particles.

Effect of pH and PMAA Content on Particles Surface Charge

The zeta potentials of the nanoparticles are summarized in Table 4 andFIG. 8B. The data show that all nanoparticles have negative surfacecharges which increase with increment of the pH of the medium from 2 to7 due to the ionization of the carboxylic acid groups associated withthe nanoparticles. Zeta potential is the charge at the electrical doublelayer, created by ions of the liquid, which exists around each particle.Nanoparticles dispersed in aqueous solutions can be stabilized either byelectrostatic stabilization (surface charge) or by steric stabilization(surfactants or other molecules at the particle surface), or by acombination of both. Generally, zeta potential values beyond +/−20 mVare considered characteristics of a stable colloidal dispersion.According to the DLVO theory, aggregation occurs when attractive van derWaals forces between the particles dominate the electrostatic repulsiveforces. As shown in Table 4 and FIG. 8B, most nanoparticle products havezeta potential close or beyond −20 mV at various studied pH values andthus are expected to be colloidally stable. When the PMAA content in thenanoparticles decreases, the zeta potential also decreases. At pH 4,PMAA-g-St-4 nanoparticles have a zeta potential of −2.7 mV, which meansthat they will have some colloidal stability problem. These data,together with the more negative charges at high pH, suggest that PMAAcontributes largely to the surface charge of the nanoparticles.

Characterization of Carboxylic Acid Groups in Starch-Based Nanoparticles

FIG. 9 shows an example of the potentiometric titration of thePMAA-g-St-2 latex dispersion at C_(s)=0.05 N NaCl. Unless otherwisespecified, a stabilization time of 5 minutes were allowed between eachtitrant addition. This is a common procedure in titration ofpolyelectrolyte latex particles as the relaxation time required toattain equilibrium is normally very long compared to corresponding lowmolecular weight weak acids. The original titration data was correctedby taking into the account the contribution of free H⁺ and OH⁻, makingthe end point clearer. The correction is performed according to equation2 [26, 27]:

[V] _(pH) =[V _(NaOH)]_(pH) +[V _(H) ₊ ⁰]_(pH) −[V _(OH) ⁻ ⁰]_(pH)  (2)

Where [V_(NaOH)] is the volume of NaOH added to the dispersion and[V_(H) ₊ ⁰] and [V_(OH) ⁻ ⁰] are the volumes of HCl and NaOH added to ablank solution of the same pH as in the dispersion. With thiscorrection, assuming the same activity coefficient for H⁺ and OH⁻ in thedispersion and in the blank solution, the value of [V]_(pH) should be aconstant at an equivalent. We determined an equivalent point of 2.39 mlusing the above procedure, shown with an arrow. This value is in goodagreement with one determined from the inflection point of the titrationcurve using simple spreadsheet programming.

Using the equivalent point data from titration studies, we determinedthe MAA contents for various PMAA-g-St batches with different feedmonomer ratio. These data along with their corresponding equivalentpoint data are presented in Table 4.

pK_(a) values of the nanoparticles of various compositions were plottedagainst α. The pK₀ values were then determined by extrapolating thepK_(a) values to α=0. The pK₀ value was found to depend on starchcontent in the nanoparticles. It increased almost by 1 unit from 4.9 forPMAA-PS 80 nanoparticles to 5.8 for PMAA-PS 80-g-St-4 nanoparticles. Theintrinsic ionization constants of PMAA-PS 80-g-St-1, PMAA-PS 80-g-St-2,and PMAA-PS 80-g-St-3 particles were 5.0, 5.1, and 5.5 respectively(FIG. 9). The increase in pK₀ with increasing starch content may beexplained in terms of higher degree of hydrogen bonding between thestarch hydroxyl groups and the terpolymer acid groups. The change in theionization behavior of the terpolymer (evidenced by change in pK_(a)trend) is possibly due to lower charge density of the particles,hydrophilic nature of the starch which could promote higher affinity towater, and more rigid chain structure of starch that would result inmore expanded conformation and a higher spatial separation of ionizablegroups.

Potentiometric titration was also used to investigate the distributionof the carboxylic acid functional groups within the PMAA-g-Stnanoparticles. The gel phase of the hydrogel nanoparticles is permeableto ions. Hence, titrant ions are not restricted to aqueous bulk phase,and can diffuse into the gel phase to neutralize the functional groupswhich reside within the gel phase. The stabilization time between thebulk and gel phase depends greatly on the distribution of the functionalgroups to be titrated. Surface accessible groups require shorterequilibrium time while titratable functional groups which are buriedbeneath the surface require longer time to reach equilibrium.

Forward (base-into-acid) followed by fast backward (acid-into-base)titration studies, allowing a stabilization time of only 30 s betweeneach addition, were used to gain insight into the distribution of acidicgroups within the nanoparticles. If the aqueous and gel phases fullyequilibrate before the addition of the next volume of the titrant, theforward and the backward titration should fully overlap; however, ifequilibrium is not achieved some sort of lag time between the twotitrations must be observed. FIG. 10 shows the forward and backwardtitration curves for PMAA and two different batches of PMAA-g-St withvarious feed ratio of MAA:St. Both PMAA (FIG. 10A), and PMAA-g-Stparticles with high MAA contents (FIG. 10B) show good overlap betweenforward and backward titrations, the PMAA-g-St nanoparticles with highstarch content, on the other hand, exhibited good overlap only near thebeginning and the end of the titration (FIG. 10C). There was asignificant lag at the pH region where the titration of the acidicgroups occurred. The fast stabilization time for PMAA and PMAA-g-Stparticles with lower starch content suggests that the diffusion of H⁺ions is not hindered by the gel structure. This is possibly due toexistence of carboxylic acid groups near the particle surface. Incontrast, the rate of H⁺ addition in the PMAA-g-St gels with high starchcontent appears to be faster than the rate of H⁺ diffusion towards thetitratable groups in the gel suggesting that the mass transfer processis partly hindered by gel structure. Based on these results, it isreasonable to conclude that the carboxylic acid groups in PMAA-g-Stnanoparticles with high level of starch contents are less accessible tothe particle surface than those in PMAA and PMAA-g-St particles of lowerstarch content.

The acid strength or ease of ionization of a polyacid differs from thatof a simple acid in that each successive charge becomes more difficultto remove as the Coulombic field builds up around the polymer coil. Theacid strength of a polyacid is represented by “apparent” pK_(a) values,and is related to degree of ionization (α) according to equation 3 [40,41]:

$\begin{matrix}{{pK}_{a} = {{{pH} - {\log \left( \frac{\alpha}{1 - \alpha} \right)}} = {{pK}_{0} + {0.4343\frac{\Delta \; G_{el}}{RT}}}}} & (3)\end{matrix}$

where pK₀ is negative logarithm of intrinsic dissociation constant, R isthe gas constant, T is the Kelvin temperature, and ΔG_(el) is anelectrostatic interaction term.

The degree of ionization (α) is calculated by

$\begin{matrix}{\alpha = \frac{\lbrack V\rbrack_{pH}}{\left\lbrack V_{eq} \right\rbrack}} & (4)\end{matrix}$

where [V_(eq) ] is the equivalent point volume.

Equation 3 describes pK_(a) in terms of the sum of a non-electrostaticterm (pK₀) and an electrostatic interaction term (ΔG_(el)). In FIG. 11the pK_(a) values of nanoparticles of various compositions are plottedagainst a. The pK₀ values are determined by extrapolating the pK_(a)values to α=0. The pK₀ of PMAA nanoparticles was found to be 4.9. Thisvalue increased almost by 1 unit by increasing the starch contents. Infact, pK₀ of 5.8 was calculated for PMAA-g-St-4 nanoparticles. Theintrinsic ionization constant of PMAA-g-St-1, PMAA-g-St-2, andPMAA-g-St-3 particles was 5.0, 5.1, and 5.5 respectively. Theexperimental value of the pK₀ for PMAA is in good agreement with that oflinear PMAA and also isobutylic acid perhaps indicating that themajority of carboxylic acid groups at the latex surface have the sameenvironment as in bulk water. As described above, the nanoparticles withlower PMAA content have some of their COOH groups buried beneath thesurface. This may decrease the dielectric constant in the vicinity ofthose carboxylic acid groups and increase the pK₀ values.

The increase in the starch content changed the ionization behavior ofnanoparticles (FIG. 11). The pK_(a) values of PMAA and PMAA-g-St withhigh MAA contents increased sharply initially with increase in degree ofionization. The pK_(a) values plateau around 25% ionization and start toincrease after 40% ionization. This behavior has been documented byother researchers as well, and is attributed to compact/extended coiltransformation of the PMAA. Generally, high charge density of the PMAAparticles coupled with their compact structure at low ionization degreeslead to rapid initial increase in pK_(a) values with extent ofionization. To minimize the strong electrostatic repulsive forces thepolymer undergoes a conformational change to more extended coilarrangement. The PMAA-g-St particles with higher starch content showeddifferent pK_(a) profile. The pK_(a) is significantly higher at lowionization degrees; however, there is almost no increase in the apparentdissociation constant up to 50% ionization. The acid groups appear tobehave as isolated units in this ionization region, producing pK_(a)curves with little slopes. This maybe explained in terms of lower chargedensity of the particles as well as hydrophilic nature of the starchpromoting higher degree of compatibility with the solvent (water) thatwould result in more extensible conformation and a higher spatialseparation of ionizable groups. However, the pK_(a) values start toincrease above 50% ionization due to higher electrostatic repulsiveforces.

Effect of Processing Parameters on Particle Size and pH Sensitivity

FIG. 12A shows the effect of SDS concentration on particle size andphase transition. The diameter of the PMAA-g-St particles decreased asthe surfactant content increased. The amphiphilic structure of the SDSsurfactant helps to stabilize the polymer particles in aqueous solutionsand thus making it possible for polymer chains to form smallerparticles. The effect of the surfactant amount on the particle size wassignificant. For example, as SDS changed from 0.17 to 0.69 mmol, theparticle size changed from 591 to 298 nm. The SDS levels of below 0.17mmol (0.05 g) resulted in particle aggregation (annotated by an arrow).Because the PMAA-g-St copolymer is negatively charged on account ofionization of COOH groups and SDS is an anionic surfactant, the absorbedSDS onto the particle surface helps to disperse the particles in waterpreventing particle aggregation. The ratio of the particle diameter atpH=7.4 to the particle diameter at pH=4 (D_(7.4)/D₄) was used to measurethe pH responsiveness. The ratio decreased at low SDS levels; however,this is due to poor stability of particles with reduced amount of SDS atlow pH values which leads to particle aggregation and misleadinglyhigher readings by DLS.

The effect of increase in PS 80 concentration on particle size and pHresponsiveness is presented in FIG. 12B. The increase in PS 80 amountincreased the particle size slightly. The mean particle size increasesfrom 238 nm at 0.13 mmol of PS 80 to 300 nm at 0.27 mmol PS 80. Furtherincrease in PS 80 levels did not affect the particle size. Increasing PS80 concentration also resulted in reduction in pH sensitivity ofparticles. As discussed previously, PS 80 can participate in thepolymerization reaction by free radical formation as well as through itsdouble bonds; hence it can potentially promote the cross-linking of thepolymer chains. Possibly, by increasing the PS 80 concentrations, theintra and inter cross-linking of the particles are increased leading toreduction in pH sensitivity of the nanoparticles.

As the total monomer concentration was increased from 0.156 mol/1 to0.41 mol/1, the average particle diameter increased from 298 to 788 nm(FIG. 12C). When the monomer concentration was further increased to 0.61mol/L, a dispersion of broad particle size distribution was obtained(data not shown). Further increase in monomer concentration resulted inmassive particle aggregation. An increase in monomer concentrationgenerally causes an increase in final particle size as it affects thenucleation process in many ways. First, the grafted polymer chains canstay longer in the continuous phase due to increased solvency of thisphase. As a result, the oligomers grow to a longer chain length beforeprecipitation. Second, the propagation rate of the oligomer chainsincreases. Also the adsorption rate of the stabilizers decreases becauseof the change in solvency of the medium. All of these effects contributeto an increase in the average size of particle nuclei. Interestingly,the pH sensitivity was not significantly affected as a result of changein monomer concentration in the feed.

FIG. 12D shows the effect of cross-linker molar ratio, X, on particlesize and pH sensitivity. The cross-linker molar ratio was calculatedusing the following equation:

$\begin{matrix}{X = \frac{{mol}\mspace{14mu} {of}\mspace{14mu} {cross}\text{-}{linker}}{{mol}\mspace{14mu} {of}\mspace{14mu} {total}\mspace{14mu} {monomer}}} & (5)\end{matrix}$

The particle size increased as a result of increase in cross-linkermolar ratio (X). It can be postulated, that at higher cross-linkinglevels more polymer chains can be cross-linked resulting in largerparticles. Also, there is a higher probability of cross-linking andparticle diffusion among individual smaller particles to form largerones. The magnitude of volume phase transition was reduced by increasingthe cross-linking levels. The content of cross-linker has a directeffect on the cross-linking density and the mesh size of the hydrogels[4], thus the cross-linker content has a great effect on the swellingbehavior of the hydrogels. With increase in cross-linker level, thepolymer chain length between the cross-links decreased; as a result, theelastically retractile force which restricts the gel swelling increaseddramatically. This explains the reduction in particles pH responsivenessat higher cross-linking levels.

A one-pot aqueous dispersion polymerization method to synthesizePMAA-g-St nanoparticles has thus been exemplified. Dependence ofparticle size and pH responsive swelling of the nanoparticles onsynthesis parameters e.g., MAA/St ratio, surfactant concentration,cross-linker concentration, and total monomer concentration. Adjustmentof these parameters shows production of PMAA-g-St nanoparticles withvarying particle sizes and pH responsiveness. PS 80 was found toparticipate in the polymerization making the product a terpolymer. Thepolysorbate also plays a role in the formation of stable nanoparticles.Presence of starch in the polymerization also appears to impart moreuniform particle size distribution. Depending on the MAA/St ratio, thenanoparticle can undergo up to ten-fold change in volume when medium pHchanges between 7.4 and 4.0.

The foregoing examples illustrate embodiments of the invention,particularly directed to the synthesis and characterization ofnanoparticles.

Production of a nanoparticle includes solubilising a polymer backbone.In the examples, the backbone is provided by starch having a molecularweight in the range of from about 2,600 to about 4,500 Da. As mentionedabove, starch is a biocompatible, biodegradable, non-toxic polymer thatexists in nature. Starch is composed of glucose units linked byglycosidic bonds. The main components of natural starch are amylose andamylopectin. In preferred embodiments, monomeric units making up thepolymer backbone bear hydroxyl groups with a degree of substitution ofbetween 0.5 and 3. This means that on average the monomeric units in thebackbone have on average 0.5 to 3 hydroxyl groups, as they occur in thepolymer. Amylose, for example, which is a linear glucose polymer thushas a degree of substitution of about 3. The degree of substitution canbe in the range from about 1 to about 3, or from 2 to about 3, or it canbe about 1, about 2, or about 3. The polymer backbone thus has multiplehydroxyl groups, so is said to be polyhydroxylated. A monomeric unit canbe, for example, one or more of a pentose or hexose (e.g., glucose), soit can have 5 or 6 carbons per monomeric unit of the backbone.Preferably, the backbone has 3, 4, 5, 6 or 7 carbons per monomer, morepreferably, 5 or 6, most preferably, 6. Examples of relatively highmolecular weight polysaccharides (as opposed to e.g., di- ortrisaccharides) include callose, laminarin, chrysolaminarin, xylan,arabinoxylan, mannan, fucoidan and galactomannan. Polysaccharides thatcan be readily broken down in the body, such as amylose can be used forto take advantage of their in vivo behavior, but less digestiblepolysaccharides such as cellulose can also form nanoparticles of theinvention. Naturally occurring starches include maize starch, potatostarch, sweet potato starch, wheat starch, sago palm starch, tapiocastarch, rice starch, soybean starch, arrow root starch, amioca starch,bracken starch, lotus starch, waxy maize starch, and high amylose cornstarch.

Production of a nanoparticle of the invention includes graftpolymerizing a monomer to the polymer. In the examples, methacrylic acidwas grafted onto starch. Methacrylic acid is an α,β-unsaturatedcarboxylic acid, and the polymerization production process of theexamples is known as free radical graft polymerizing. Suchpolymerization processes are typically conducted in the presence of afree radical initiator. As the graft polymerizing process proceeds themonomer molecules grow into chains in which the C—C bonds form intocarbon based chains and the carboxyl groups from side groups of thechains. The carboxyl group is a Bronsted acid which, depending upon itsenvironment can lose a proton (H⁺) so exist as a carboxylate group (CO₂⁻). So when the number of carboxyl groups on a chain is referred to, theform of the carboxyl group, be it CO₂H or CO₂ ⁻, is not taken intoaccount. The acid behaviour of the carboxyl groups in the nanoparticlecontributes to the properties of a nanoparticle, particularly itsbehavior at different pHs, and this is discussed elsewhere. When themonomer is an α,β-unsaturated carboxylic acid, the chain formed as partof the nanoparticle contains a carbon based chain having a carboxylgroup on alternating carbons.

In the preferred “one-pot” synthesis of the invention, the polymerizingreaction is conducted in the presence of ethoxylated molecules thatparticipate in the polymerizing reaction i.e., form covalent bonds withthe forming side chains. In the examples, the ethoxylated molecules arepolysorbate 80, commercially available as Tween® 80. The wordpolysorbate describes a group of compounds having the structure:

For a given polysorbate, w+x+y+z equals a given number “n” and “R” isone or more of a fatty hydrocarbyl group. The group —O(O)C—R typicallycorresponds to a naturally occurring fatty acid. In the case ofpolysorbate 80, n=20 and the R-group is the same as the R-group in oleicacid:

In fact, another name for polysorbate 80 is polyoxyethylene (20)sorbitan monooleate reflecting the presence of the sorbitan core,oxyethylene groups (—CH₂—CH₂—O—) and the oleic acid linked to thesorbitan via an ester linkage, and indicating the value of n.

As described in the Examples, the oleic acid R-group of the polysorbate80 becomes covalently linked to the growing side chain during graftpolymerization of the monomer, and the polyethoxylated portions come toreside at the exterior surface of a nanoparticle. The invention includesethoxylated molecules that display this behaviour during synthesis ofthe nanoparticle: the polymerizing step is conducted in the presence ofthe ethoxylated molecules to covalently link the ethoxylated moleculesto the polymeric chains. Preferably, the polymerizing step is conductedin the presence of polyethoxylated molecules to covalently link thepolyethoxylated molecules to the forming chains and the polymerizedproduct forms into a nanoparticle with polyethoxylated moieties on theexterior of the nanoparticle.

As indicated elsewhere, polyethoxylate portions impart useful practicalcharacteristics to nanoparticles of the invention. The number ofoxyethylene units or groups in an ethoxylated molecule incorporated intoa nanoparticle can be 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21,22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39or 40. It is to be noted that a given polysorbate is often a mixture ofmolecules, so these numbers refer to averages. Preferably, thepolyethoxylated molecule is a sorbitan-based molecule. More preferably,it is a polysorbate.

As characterized for nanoparticles of the invention, the C═C(unsaturation) of the R-group of the polysorbate participates in thepolymerization of the nanoparticle synthesis. The polyethoxylatedmoieties thus become covalently bound to the polymer chain that formsduring the synthesis and are covalently bound to the chains of thenanoparticle formed. Polyethoxylated sorbitan having aR(C9-C31)-C(O)O-group wherein the sorbitan is linked to the secondpolymer through a C—C covalent bond of the R(C9-C31)-C(O)O-group duringthe graft polymerization is thus an embodiment of the invention.Preferably, the sorbitan is a polysorbate in which the total number ofoxyethylene units is at least 10. It is also preferable that theR(C9-C31)-C(O)O-group contains at least one C—C unsaturation whichreacts to form the C—C covalent bond in the step of polymerizing. TheR(C9-C31)-C(O)O-group can be any of C9, C10, C11, C12, C13, C14, C15,C16, C17, C18, C19, C20, C21, C22, C23, C24, C25, C26, C27, C28, C29,C30, C31. Fatty acids (R—CO₂H) having a total number of carbons that isan even number are more common meaning that R-groups in this situationhaving an odd number are more common which can result in those beingpreferred.

There are fatty acids other than the oleic acid component of polysorbate80 that contain unsaturations, such as linoleic acid, arachidonic acid,myristoleic acid, palmitoleic acid, sapienic acid, elaidic acid,vaccenic acid, linoelaidic acid, α-linolenic acid, eicosapentaenoic,erucic acid, etc. It may be found advantageous under variouscircumstances for a nanoparticle to have incorporated thereinto one ormore polysorbates based on one or more of these fatty acids.

As described in the Examples, the relative amounts of polymer andmonomer of the graft polymerizing step can vary to obtain nanoparticleshaving different polymer/monomer ratios. In the context of thenanoparticle, monomer molecules are part of a chain formed duringpolymerization, and so can also be referred to as monomeric units. Theexamples show nanoparticles in which the molar ratio of monomeric unitsof the polymerizing monomer to monomeric units of polymer backbone(i.e., MMA/St) is 0.6 to 4.7. It is possible to obtain other ratiosbetween about 0.1 and about 10, or 0.2 and 9.0, or 0.2 and 8, or 0.2 and8.0, or 0.2 and 7.0, or 0.3 and 7.0, or 0.3 and 6.0, or 0.4 and 6.0, or0.4 and 5.0, or 0.4 and 4.0, or 0.4 and 3.0, or 0.5 and 6.0, or 0.6 and6.0, or 0.7 and 6.0, or 0.8 and 6.0, or between 1 and 5.0, or to obtaina ratio of e.g., about 0.1, about 0.2, about 0.3, about 0.4, about 0.5,about 0.6, about 0.7, about 0.8, about 0.9, about 1, about 1.5, about 2,about 2.5, about 3, about 3.5, about 4, about 4.5, about 5, about 5.5,about 6, about 6.5, about 7, about 7.5, about 8, about 8.5, about 9,about 9.5 or about 10.

Also described in the Examples, are nanoparticles in which relativeamounts of the polyethoxylate molecules and monomeric units of thepolymerized monomer are varied, again by varying the amounts ofpolysorbate 80 and MAA during nanoparticle synthesis. For those particlecomponents, molar ratios of ethoxylated molecules to monomeric units ofthe polymerized chain from about 0.003 to about 0.01 were indicated. Itis possible to obtain other ratios i.e., between about 0.0005 and 1,between about 0.0006 and 0.1, between about 0.001 and 0.1, between about0.001 and 0.05, between about 0.001 and 0.04, between about 0.002 and0.04 between about 0.002 and 0.03, between about 0.002 and 0.02 orbetween about 0.003 and 0.01 or to obtain a ratio of e.g., about 0.0005,about 0.0007, about 0.0009, about 1, about 0.9 about 0.8, about 0.7,about 0.6, about 0.5, about 0.4, about 0.3, about 0.2, about 0.1, about0.005, about 0.006, about 0.007, about 0.008, or about 0.009.

The graft polymerization of the examples utilizedN,N′-Methylenebisacrylamide was used. In the examples, the molar ratioof the polymerizing monomer, MAA and the cross-linker, MBA, ranged fromabout 3:1 to about 7:1. The amount of the monomer used in thepolymerizing step can be between 1 and 20 times the amount of thecross-linking agent, on a molar basis, or it can be between 1 and 15, orbetween 1 and 10, or between 2 and 10, or between 2 and 9 or between 2and 8, or between 2 and 7, or between 2 and 6, or the amount of themonomer can be between 3 and 6 times the amount of the cross-linkingagent, on a molar basis.

Applications and Uses of Nanoparticles

Various modifications of nanoparticles of the invention have beencreated demonstrating their useful in a number of applications,particularly related to the medical arts. Modified version of thenanoparticles are possible to obtain, both during synthesis of thenanoparticles, or subsequent to their formulation.

In one application, described in greater detail below, usefulness ofnanoparticles of the invention as a drug delivery agent is demonstratedutilizing the drug doxorubicin. Doxorubicin, a member of theanthracycline ring antibiotic family, is a well-known anticancer drughaving broad spectrum antitumor activity in a variety of human andanimal solid tumours [42, 43]. The drug, however, has a very narrowtherapeutic index and its clinical use is hampered by severalundesirable side effects such as cardiotoxicity and myelosuppression[44-46]. Another limitation is that the drug is a known p-glycoprotein(P-gp) substrate. P-gp prevents intracellular accumulation of manyanticancer agents and, hence, causes a reduction in their cytotoxicactivity principally by preventing active uptake and increasing cellularefflux of positively charged amphipathic drugs in an ATP-dependentmanner. Overexpression of P-gp is thought to be one of the mainmechanisms of multi-drug resistance in cancer cells [47-50].

Association of doxorubicin with a suitable nanoparticulate system mightaddress some of the limitations associated with doxorubicin chemotherapy[51-55]. Targeted delivery of drugs by incorporating them intoappropriate nano-carrier system modifies the biodistribution andpharmacokinetics of the drug in vivo [56]. In principle, accumulation ofdrug-loaded nanoparticles in tumours can be achieved by a nonspecifictargeting process known as enhanced permeability and retention (EPR)effect [38, 57]. A leaky vasculature and limited lymphatic drainage,typical of tumour and missing in normal tissue, result in theaccumulation of macromolecular drug carrier systems in the interstitialspace of a large variety of tumours. The association of doxorubicin witha colloidal carrier such as a nanoparticle could potentially overcomemultidrug resistance (MDR). It has been hypothesized that P-gprecognizes the drug to be effluxed out of the tumor cell only when it ispresent in the plasma membrane and not in cases where it is located inthe cytoplasm or lysosomes after its endocytosis [53, 54, 58, 59].

Due to the presence of epithelia-like tight junctions lining the braincapillary endothelium, referred to as the blood-brain barrier (BBB),more than 98% of all new potential brain drugs are ineffective as theyare unable to cross the BBB. In the areas of brain delivery of drugs,there have been a number of approaches to overcome the BBB, such as theosmotic opening of tight junctions, usage of prodrugs, and carriersystems like targeted antibodies, liposomes, and nanoparticles [60-63].For almost a decade, surfactant-coated nanoparticles have been reportedto successfully transport drugs across the BBB. Nanoparticle-mediateddrug transport depends in part on the coating of the particles, notablywith polysorbates, especially polysorbate 80 (Tween 80) [63-67].Overcoating with these materials leads to the adsorption ofapolipoprotein E (ApoE) from blood plasma onto the nanoparticle surface.The particles then seem to mimic low density lipoprotein (LDL) particlesand interact with the LDL receptor, leading to their phagocytosis by theendothelial cells lining the BBB. The drug or imaging probesencapsulated in the nanoparticles may then be transported into thesecells through receptor-mediated transcytosis [63, 68, 69]. In addition,it has been suspected that processes such as modulation of tightjunctions or inhibition of the P-glycoprotein efflux system also occurs,resulting in brain uptake of nanoparticles. To date, many differentsurfactants have been evaluated. Only polysorbate 80 overcoat has beendemonstrated to produce a brain targeting effect following intravenousadministration, suggesting a specific role for polysorbate 80 in braintargeting [63]. Efficacy of overcoating with polysorbate 80 is limiteddue to the fact that the absorbed surfactant on the surface of thenanoparticles can be desorbed in vivo due to replacement by the bloodcomponents with high affinity to the particles surface.

In another application, usefulness of nanoparticles of the invention isdemonstrated in the area of medical diagnostics, examples describedbelow, showing use in the areas of magnetic resonance imaging (MRI), andfluorescent probes.

Magnetic resonance imaging is a known powerful diagnostic and analyticalmodality which provides non-invasive 3D visualization of anatomy withinan arbitrary plane with superb soft tissue contrast, and enablesinvestigation of vascular and tissue physiology and pathology usingquantitative biomarkers [70, 71]. Soft tissue contrast in MR images ismulti-factorial, depending on the imaging method, protocol and therelaxation time constants of tissues (e.g. T₁, T₂). Exogenousparamagnetic contrast agents e.g., Gd³⁺, Fe³⁺, and Mn²⁺ complexes arecommonly used which alter the relaxation rates of the surrounding waterprotons to accentuate vascular and soft tissue contrast in certainapplications [72].

Gadolinium (Gd³⁺) is the primary paramagnetic molecule used for MRI dueto high relaxation efficiency and magnetic moments [73-75]. However,gadolinium in its free form is highly toxic to the biological systems,hence Gd⁺³ contrast agents are formulated as stable, water-solublechelates to improve their clinical safety profile [76-78]. The contrastenhancing capacity, termed ‘relaxivity’, of a Gd³⁺ based contrast agentis directly proportional to the number of exchangeable water moleculesin the inner coordination sphere of the Gd³⁺ ion [72-74]. Unfortunately,the complexation of Gd³⁺ by organic chelators reduces the number ofinner sphere water molecules. Hence, one of the major challenges in thedesign of Gd³⁺ based MRI contrast agents is how to increase theirrelaxivity while minimizing their toxic side effects.

Clinically used Gd³⁺ contrast agents such asdiethylenetriaminepentaacetic acid gadolinium (Magnevist®) anddiethylenetriamine pentaacetic acid bismethylamide gadolinium(Omniscan®) are non-toxic yet exhibit relatively low T₁ relaxivities,rapid vascular extravasation into the extra-cellular space, non-specificdistribution to the whole body, and fast renal clearance. As a result,in clinical practice, multiple injections or infusion of Gd³⁺ contrastagents are required for a single diagnosis [79]. In contrast, non-toxicmacromolecular MRI contrast agents such as PEG, poly(L-lysine),poly(glutamic acid), dendrimers, dextran, and supramolecular systemsincluding liposomes, micelles, and other such systems exhibit higher T₁relaxivities and longer residential periods in the bloodstream [80-90].These macromolecular and supramolecular systems also enable passivetargeting of tumors owing to leaky vasculature and under-development ofsurrounding lymph vessels known as the enhanced permeability andretention (EPR) effect [57, 91].

Starch-based derivatives such as carboxymethyl starch are already usedin humans as a plasma expander; it is generally well tolerated incomparison with dextran, due to its lower immunologic potential. Unlikealbumin, carboxymethyl starch contains no peptide components that may beimmunologically active and may induce antibody production. [92]

As exemplified herein, starch-based nanoparticles, containingpolymethacrylic acid-grafted-starch-DTPA (PMAA-g-St-DTPA) can besynthesized in a simple one-pot synthesis process in water. The polymercan bind to gadolinium with high affinity. The synthesis process can betailored to obtain polymers of suitable molecular weight which issoluble in physiological pH.

Due to abundance of hydroxyl and carboxylic acid groups owing to starchand methacrylic acid components of the system, a wide range of drugs,targeting moieties, and fluorescence probes can be conjugated to thepolymer.

Example 2 St-g-PMAA-P80 Nanoparticles for Delivery of Anticancer DrugDoxorubicin

The ability of the nanoparticles to load doxorubicin (cationic,Mw=579.98 g/mol) has evaluated using drug uptake studies. Fifty mg oflyophilized nanoparticles is suspended in 10 ml of distilled deionizedwater (DDIW). The drug is added at a concentration of 0.1-5 mg/ml to thesuspension and allowed to adsorb onto the nanoparticle for 24 hrs. Theparticles are then ultracentrifuged at 30000 rpm for 30 minutes, and theamount of drug in the supernatant assayed using a UV spectrophotometer.Subsequently, the amount of drug loaded into the particles is calculatedby subtracting the final drug concentration from the initial drugconcentration in the loading solution. The drug loading content andentrapment efficiency are then calculated using the following equations:

${{Drug}\mspace{14mu} {loading}\mspace{14mu} {content}\mspace{14mu} \%} = {\frac{{Wt}\mspace{14mu} {of}\mspace{14mu} {drug}\mspace{14mu} {loaded}}{{{Wt}\mspace{14mu} {of}\mspace{14mu} {drug}} + {{Wt}\mspace{14mu} {of}\mspace{14mu} {nanoparicles}}} \times 100\%}$${{Drug}\mspace{14mu} {loading}\mspace{14mu} {efficiency}\mspace{14mu} \%} = {\frac{{Wt}\mspace{14mu} {of}\mspace{14mu} {drug}\mspace{14mu} {loaded}}{{Initial}\mspace{14mu} {Wt}\mspace{14mu} {of}\mspace{14mu} {drug}\mspace{14mu} {in}\mspace{14mu} {the}\mspace{14mu} {loading}\mspace{14mu} {solution}} \times 100\%}$

The particle size and surface charge of PolyGd-Dox nanoparticles weredetermined by DLS and electrophoretic mobility measurements. Thenanoparticles dispersion was diluted to 0.5 mg/ml using PBS with pH=7.4and ionic strength of 150 mM (size measurements) or 10 mM (ζ-potentialmeasurements). All size and ζ-potential measurements were performedusing Malvern Zetasizer Nano ZS (Worcestershire, UK). Each measurementwas performed in triplicate and the averages±standard deviations arereported (Tables 5A and 5B).

The present data indicate that PMAA-PS 80-g-St nanoparticles are able toload substantial amounts of Dox with no loss of their colloidalstability (FIG. 13). Indicated in FIG. 14 is XRD spectrum of A)doxorubicin in native form, B) PMAA-PS 80-g-St nanoparticles, C)Doxorubicin loaded nanoparticles (LC-50%), D) doxorubicin-loadednanoparticles (LC=50%) after 6 months storage at room temperature. Fordoxorubicin clear peaks are visible in the diffractogram indicating thepresence of crystalline phase in the native form whereas nanoparticlesshow a typical amorphous pattern. Absence of peaks in the diffractogramsof doxorubicin loaded nanoparticles indicates the phase transformationof crystalline doxorubicin to amorphous doxorubicin.

A frequent limitation of nanoparticulate drug delivery systems is theamount of drug that can be carried. For example, polyalkylcyanoacrylate(PACA) nanoparticles exhibited 3.7% loading content for doxorubicin withthe loading efficiency of 74% [93]. Doxorubicin loading content andloading efficiency were 5% and 47% respectively inpoly(lactic-co-glycolic acid) (PLGA) nanoparticles [94]. Table 2demonstrates the loading efficiency, size and zeta potential forparticles of various loading contents. St-g-PMAA-P80 nanoparticles ofthe present invention have a high loading capacity, and the loadingefficiency remains virtually unchanged and close to 100% even at thehighest loading content. Hence, nanoparticles with various drug loadscan be prepared readily by varying the nanoparticle-to-drug ratiowithout noticeable compromise of loading efficiency and particle sizeand stability. The high loading efficiency reduces waste of expensivedrugs. Having a delivery system with high loading content makes itpossible to use a smaller quantity of carrier material, which isdesirable for repeated injections. Moreover, having particles with highloading content may potentially improve the treatment efficacy asdesirable drug levels in target organ and tissues can be achievedprovided small amounts of the drug-loaded particles reach their site ofaction.

ITC and FTIR were used to gain insight into the interaction ofdoxorubicin with the nanoparticles. FTIR data provided evidence forstrong electrostatic interactions between carboxylic groups ofnanoparticles and amine groups of Dox. Also, there is some evidence forpossible hydrogen bonding between the OH groups of starch and the OH andNH₂ groups of Dox. The ITC results showed that there is a very stronginteraction between Dox and the carboxylic acid groups of thenanoparticles with the maximum stoichiometry of 1. The magnitude of theinteraction is strongly dependent on the pH and ionic strength of themedium (FIGS. 1 and 15).

The effect of pH on in vitro release of dox from the particles wasinvestigated using the dialysis method (FIG. 16). The particlesexhibited pH-dependent sustained release of dox. The nanoparticlesexhibit significantly slower drug release at pH 7.4 and 6 compared to pH5. There is little or no burst release at pH 7.4 with less than 20% ofthe drug being released after 90 hrs. The release rate graduallyincreases at pH 6 with close to 35% of the loaded drug being releasedafter 90 hrs. As the pH drops to 5, there is a significant increase inthe drug release rate. This is characterized by initial burst of 20% inthe first 8 hours, followed by relatively slower release rates leadingto more than 90% of drug being released after 90 hrs. The pH-dependentdrug release from the St-g-PMAA-P80 nanoparticles can be explained interms of the extent of the drug-polymer interaction as well as the pHdependent volume change of the particles. Having a nanoparticulate drugdelivery system which exhibits significantly faster drug release inacidic environments will serve as a tool to minimize the drug exposureto healthy tissues while increasing the drug levels in tumor site. Ithas been shown that human tumors exhibit acidic pH states that rangefrom 5.7 to 7. Rapidly growing tumor cells have elevated rates ofglucose uptake but reduced rates of oxidative phosphorylation leading tolactic acid accumulation and subsequent acidity of tumourmicroenvironment. This persistence of high lactate production by tumorsin the presence of oxygen, termed Warburg's effect, provides a growthadvantage for tumour cells in vivo. In addition, insufficient bloodsupply and poor lymphatic drainage, characteristics of most tumours,also contribute to the acidity of tumor microenvironment. TheSt-g-PMAA-P80 nanoparticles can potentially exploit this pH gradient toachieve high local drug concentrations and to minimize overall systemicexposure.

Example 3 PMAA-PS 80-g-St Nanoparticles for Delivery of CaspaseInhibitor Peptides

Caspase inhibitor peptides such asN-benzyloxycarbonyl-Asp(OMe)-Glu(OMe)-Val-Asp(OMe)-fluoromethyl ketone(Z-DEVD-FMK) have been demonstrated to reduce neuronal cell death[95-97], but are unable to cross the blood-brain barrier (BBB).

For effectively loading poorly water-soluble drugs, such as caspaseinhibitor peptides, a lipid chain was introduced to the polymer. In atypical reaction, myristic acid (10 mg, 0.043 mmol) was incubated withEDC (34 mg, 0.175 mmol) and NHS (40 mg, 0.350 mmol) in 5 ml of DMSO for1 h at room temperature, and PMAA-PS80-g-St (200 mg) dissolved in 5 mlof DMSO/H₂O mixture was added. The mixture was stirred at roomtemperature for 24 h and then purified by dialysis against DDIW (2 L,MWCO=12000 kDa) for 48 h, changing the dialysate every 12 h. The solidlipid-polymer was obtained by freeze drying. Z-DEVD-FMK was used as amodel caspase inhibitor peptide. To prepare the self-assemblednanoparticles, 10 mg of lipid-polymer was dissolved in 2.0 ml of DDIwater. The lipid polymer solution was then placed in an ice bath, andwhile under ultrasonication, using a Hielscher UP 100H probeultrasonicator (Hielscher USA, Inc., Ringwood N.J., USA), 200 μL (5×40μL) of peptide solution (1 mg/ml in CH₃CN/H₂O (2/8, v/v) mixture) wasadded in small increments to the lipid polymer solution every 10seconds. The particle size of peptide-loaded NPs was measured by using aZetasizer nano system to be 37 nm. The loading efficiency was foundhigher than 91%.

Example 4 Particle Uptake by MDA-MB435/LCC6 Human Breast Cancer Cells

The uptake of the fluorescamine labeled nanoparticles by MDA-MB435/LCC6cells was investigated using fluorescence microscopy and flow cytometry.Fluoresceinamine (FA) was covalently linked to the NPs. Briefly, 200 mgof the NPs were dispersed in 20 ml of DDIW, followed by addition of 50mg of NHS and EDC. After 45 minutes, the reaction was started by adding10 mg of FA. The mixture was protected from light and stirred for 24 hrsat room temperature. The pH was then adjusted to 7.4 and the particleswere then washed three times followed by centrifugation to remove anyunreacted dye.

The fluorescamine was covalently bound to the particles and thereforethere was no leakage of the dye from the particles. After incubation thecells were washed exhaustively with cold PBS to ensure that the looselybound particles to the cell surface are washed off Serial z-sections ofthe cells, each 1 μm in thickness, demonstrated fluorescence activity inall the sections between 3 and 15 μm from the surface of the cells,indicating that the nanoparticles were both bound to the cell surface aswell as internalized by the cells (data not shown). Staining of thenuclei (DAPI) and cell membrane (Vybrant™Dil) prior to incubation of thecells with nanoparticles allowed for the discrimination of particleuptake by membrane-bound vesicle pathways (i.e. endocytosis), or throughpenetration of the cell membrane. If the particles enter the cell bypassive diffusion, there would be expected to be no membrane boundvesicles surrounding them, and as a result the fluorescence signal fromthe nanoparticles would not be expected to co-localize with the signalfrom intracellular vesicles (Vybrant™ DiI). However, if nanoparticleswere taken up into the cell via endocytosis-like mechanisms, amembrane-bound vesicle would surround the particles, and the signalco-localization from the labelled nanoparticles and stained membranevesicles would be expected. FIG. 17A demonstrates particle uptake by thewild-type (MDA MB435-WT) and multidrug resistant (MDA MBA435-MDR1)cells. In the absence of nanoparticle incubation with the cells, therewas no signal using the FITC filter, and there were limited numbers ofsmall, intracellular fluorescent foci of internalized Vybrant™DiI-stained cell membrane representing membrane-bound vesicles (Controlfor both wild type and MDR cells). However, following incubation withnanoparticles for 4 hours, a greater number of larger fluorescent fociwere observed in both cell lines. These red fluorescent foci, which mayrepresent membrane-bound vesicles formed from stained cell membrane(Vybrant™Dil), aligned with the fluorescent green foci observed from thenanoparticles signal (FITC). As shown in FIG. 17B, the nanoparticlesloaded with Gd³⁺ appear as electron-dense deposits. This suggests thatSt-g-PMAA-P80 nanoparticles are taken up by the cells via membrane-boundvesicles, and shuttled to the perinuclear region of the cytosol in bothwild type and resistant human breast tumor cells.

Flow cytometry was used to measure the cellular uptake of theSt-g-PMAA-P80 nanoparticles in MDA 435 cell line (both WT and MDR1). Asshown in FIG. 18, the cellular level of the nanoparticles progressivelyincreased in both WT (A,B) and MDR1 (C,D) cells with incubation time at37° C., and did not reach saturation up to 24 hrs of incubation.Interestingly, the resistance cell line showed faster and higher extentof particle uptake compared to the wild type. The mean fluorescenceintensity for WT and MDR1 cells were 896 and 1897 respectively after onehour. These values increased to 11510 and 18574 after 24 hours. The datashow that nanoparticle uptake is relatively rapid at 37° C. as we wereable to see significant uptake within an hour. Alternatively, when thecells were incubated at 4° C., there was a significant reduction in thecellular uptake of the particles. The cells incubated at 4° C. showedonly slightly higher fluorescence intensity values compared to thebackground, which may be representing the cell surface bound particleswithout being internalized. The significant reduction in the cellularuptake of particles at low temperature, a general metabolic inhibitor,indicates that the cellular uptake of the nanoparticles is an energydependent process. Because endocytosis is an active process, uptake bythis mechanism slows at low temperature; pronounced reductions innanoparticle uptake, as observed here, are consistent withinternalization via endocytosis, rather than diffusion across the plasmamembrane.

Example 5 In Vitro Assessment of NPs Anticancer Efficacy Against WildType and Multidrug Resistant Human Breast Cancer Cell Lines

The efficacy of free Dox and Dox-loaded nanoparticles againstMDA-MB435/LCC6 breast cancer cell lines were evaluated in both wild typeand resistance cells (FIG. 19). The cells were treated with increasingconcentrations of doxorubicin or doxorubicin-loaded nanoparticles for 24hrs and 48 hrs, and the cell viability was determined using MTT assay.Both free Dox and Dox-loaded nanoparticles were equally effectiveagainst the wild-type cell line (FIG. 19A,B). All treatments elicitedcytotoxicity on wild-type cells in a dose-dependent manner. The IC50values for 24 hrs treatments were 0.34 μg/ml and 0.32 μg/ml for free Doxand the drug-loaded nanoparticles respectively. These values decreasedto 0.07 μg/ml (free Dox) and 0.06 μg/ml (nanoparticles) by increasingthe treatment length to 48 hrs. The data indicate that loading of thedoxorubicin into the nanoparticles does not result in loss of drugactivity.

The cytotoxicity of the free drug and the drug-loaded nanoparticles werealso evaluated in the MDR1 cell lines. Increasing Dox concentrations forMDR cells did not decrease the cell viability at the same magnitude asit did for the wild type. The IC50 of the free Dox in the resistancecells were 57.01 μg/ml and 7.69 μg/ml for the 24 hrs and 48 hrstreatments respectively (FIG. 19C,D). The Dox-loaded nanoparticlesperformed significantly better compared to the free drug with the IC50values of 2.99 μg/ml and 0.62 μg/ml for 24 hrs and 48 hrs incubationtimes. It appears that increasing the treatment time results in higherkilling. More importantly, the loading of the doxorubicin into thenanoparticles results in up to 19-fold reduction in IC50 values in theresistance cells.

Example 6 Synthesis of Novel DTPA-Containing St-g-PMAA-P80 Polymers andNanoparticles Preparation of Dual Mode Nanoparticles

The schematic structure of PF-NPs and SA-NPs and their preparationprocedures are illustrated in FIG. 20 and prepared as indicated below.

Preparation of the Gd³⁺ Loaded PMAA-g-St-DTPA Polymer (PF-NPs)

The PMAA-g-St-DTPA was synthesized by first conjugatingdiethylenetriaminepenta acetic acid bisanhydride (DTPA-bis-anhydride) tothe starch followed by grating polymerization of MAA.

Synthesis of DTPA-bis-anhydride:

DTPA-bis-anhydride was synthesized according to the method described byAndersen et al. [98]. DTPA (5 g, 0.0125 mole), acetic anhydride (3.62ml), and pyridine (4.61 ml) were combined in a 50 ml 3-neckedflat-bottomed reactor fitted with a thermometer, a mechanical stirrer,and reflux condenser cooled with cold water. The mixture was heated withstirring to 60° C. in an oil bath over night. The flask was rinsed withisopropyl alcohol (IPA), and the content was filtered on a Büchnerfunnel, washed with acetonitrile twice and dried over night undervacuum.

Synthesis of St-DTPA:

Soluble starch (3 g) was dissolved in 50 ml of dry DMSO followed byaddition of 1.5 g of DTPA-bis-anhydride. The solution was stirred atroom temperature for 24 hrs, dialysed against DMSO for 24 hrs, andsubsequently against water for another 24 hrs. The product (St-DTPA) wasthen dried in an oven at 50° C. overnight.

Synthesis of PMAA-g-St-DTPA polymer:

The PMAA-g-St-DTPA polymer was synthesized using a modification of aone-pot dispersion polymerization method developed previously in our lab[99]. Briefly, 1.55 g of St-DTPA was dissolved in 150 ml of distilledwater by heating at 70° C. for 30 minutes. The solution was purged withN₂ for 30 minutes to remove any dissolved oxygen. Subsequently, 0.25 gof SDS, 1.5 g of PS 80, 0.18 g KPS and 0.25 g STS were added to theSt-DTPA solution while under stirring. After 10 minutes, the reactionwas started by addition of 2 g of nitrogen purged MAA. Opalescenceappeared after 5 minutes and the reaction was continued for 8 hours at70° C. to ensure complete grafting. The product was washed extensivelywith warm water twice and extracted with methanol followed by dialysisto remove any unreacted materials and homopolymers. The purifiedparticles were then dried in a vacuum oven for 24 hours, and stored in adesiccator for future use.

Loading of Gd³⁺ onto PMAA-g-St-DTPA polymer:

The PMAA-g-St-DTPA polymer (0.5 g) was dispersed in 10 mL of DDIW water.The pH was adjusted to 6.5 using 0.1N NaOH. 10 ml of aqueous solution ofgadolinium chloride hexahydrate (10 mg/ml) was then added drop wisewhile stirring, and the pH of the reaction was kept at 6.5 with the NaOHsolution throughout the experiments. Stirring was then continued for 1hr, and the product was dialysed exhaustively against 0.9% NaCl until nofree Gd⁺³ was detected in the wash medium using the xylenol orange test[100]. The product was then freeze-dried and stored for future use. TheGd⁺³ content in the product was measured using inductively coupledplasma atomic emission spectrography (ICP-AES, Optima 7300, PerkinElmer,Shelton, USA).

DTPA bisanhydride (DTPA-A) was added to a suspension of swollenSt-g-PMAA-P80 in dry DMSO at ambient temperature. The suspension isagitated at ambient temperature for 24 hrs, and then cooled withice-water bath. Distilled water (100 ml) is added and the suspension isagitated at room temperature for 1 hr. The polymer is dialyzed againstwater for 48 hrs, and collected by ultracentrifugation at 30000 rpm for30 minutes. Alternatively, the DTPA can be covalently linked to thestarch first according to the procedure outlined above, and theresultant Starch-DTPA can be used to synthesize the St-g-PMAA-P80 usingthe method described previously. The resultant DTPA containingSt-g-PMAA-P80 can then effectively load Gd⁺³. Briefly; 0.5 gram of thepolymer is dispersed in 10 mL of DDIW water. The pH is adjusted to 6.5using 0.1N NaOH. 12.5 ml of aqueous solution of gadolinium chloridehexahydrate (10 mg/ml) is then added drop wise while stirring, and thepH of the reaction is kept at 6.5 with the sodium hydroxide solutionthroughout the experiments. Stirring is then continued for 24 hrs, andthe resulting product is purified by dialysis against 0.9% NaCl until nofree Gd⁺³ is detected in the wash medium using the xylenol orange test.The product is then freeze-dried and stored for future use. Thegadolinium content is then measured using inductively coupled plasmaatomic emission spectrography (ICP-AES).

The stability of the resultant lanthanide complexes within thebiological environments is an important consideration, as free Gd³⁺ ishighly toxic. DTPA is a strong chelator of gadolinium. TheDTPA-gadolinium complex is known to be stable in biological systems. Thesize of the nanoparticles can be adjusted by modifying the reactionparameters such as monomers concentrations, surfactant levels, etc.Alternatively, DTPA can be incorporated into the preformed St-g-PMAA-P80nanoparticles through reaction with starch hydroxyl groups. Our datashow that DTPA containing nanoparticles can form a stable complex withgadolinium (log K_(d)=17.5).

In order to obtain quantitative information about the efficiency ofGd⁺³-loaded nanoparticles as MRI contrast agents, we determined therelaxivity at 3.0 and 7.0 T. The T1 values of various concentrations ofnanoparticles were determined in vitro, and a linear fit between 1/T1and concentration was performed to obtain the relaxivity. The relaxavityvalues are listed in Tables 5A and 5B. The relaxivity for Omniscan,which is a clinically available MRI contrast agent, has been includedfor comparison. The Gd loaded St-g-PMAA-P80 showed significantly higherrelaxivity values compared to the Omniscan. The relaxivity is found tobe dependent on the magnetic field strength which is expected for themacromolecular contrast agents.

In one example, the nanoparticles were loaded with Dox. Briefly, 50 mgof lyophilized nanoparticles were suspended in 10 ml of DDIW. Dox wasadded in concentration of 2.5 mg/ml to the suspension and incubated withthe nanoparticle for 48 hrs. The particles were then ultra-centrifugedat 96,000 g for 30 minutes, and washed trice with DDIW. The PF-NPs werethen freeze-dried and store at 4° C. for future use.

Preparation of Self-Assembled Nanoparticles (SA-NPs)

The PMAA-PS 80-g-St soluble polymer was synthesized using the methoddescribed above with slight modifications. There was no cross-linker(MBA) and the amount of PS 80 was increased to 1 gram.

Next, Hilyte Fluor™ 750 was covalently linked to the polymer using themethod described above. Finally, to prepare the self-assemblednanoparticles (SA-NPs), 8 mg of the polymer was dissolved in 1.8 ml ofsterile 5% dextrose. The polymer solution was then placed in an icebath, and while under ultrasonication, using a Hielscher UP 100H probeultrasonicator (Hielscher USA, Inc., Ringwood N.J., USA), 170 μl (5×34μl) of doxorubicin solution (12 mg/ml in 5% dextrose) was added in smallincrements to the polymer solution every 30 seconds. The ultrasonicationcontinued for another 10 minutes. Addition of the Dox resulted inspontaneous formation of nanoparticles. The SA-NPs were then passedthrough ion exchange resins, Sephadex G50 fine (GE Healthcare,Piscataway, N.J., USA) to remove unbound Dox.

As illustrated in the schematic in FIG. 20, in the case of PF-NPs, theNIR fluorescent probe was covalently bound and the drug was loaded intothe preformed cross-linked PMAA-Ps 80-g-St nanoparticles. The SA-NPswere spontaneously formed in aqueous medium with covalent linkage of thedye followed by addition of the Dox to the soluble PMAA-PS 80-g-Stpolymer. The linkage of HiLyte Fluor™ 750, and ionic complexation of thedoxorubicin to the carboxylic acid groups of the PMAA-PS 80-g-St polymerare believed to increase the overall hydrophobicity, resulting in theformation of dense nano-structures which is stabilized by the presenceof PS 80 and ionic repulsive forces on the particle surface due topresence of negatively charged carboxylic acid groups.

SA-NPs and PF-NPs exhibit particle sizes of 62±5 nm (PdI=0.12) and 137±3nm (PdI=0.07) respectively (FIGS. 23D-E). TEM photographs illustratethat the particle size are in good agreement with the DLS data, andsuggest different morphology between SA-NPs and PF-NPs. PF-NPs arenearly spherical with a porous cotton ball structure while the SA-NPsare less spherical and exhibit a more compact overall morphology. Thesurface charge of the nanoparticles was found to be negative, with4-potential values of −38±1 (SA-NPs) and −35±5 (PF-NPs).

Example 7 Cytotoxicity of St-DTPA-g-PMAA-P80 Chelated Gd⁺³ vs. Free Gd⁺³Cell Viability

As a preliminary assessment of the safety of the nanoparticles for invivo use, their toxicity was assessed against free gadolinium solutionusing isolated rat hepatocytes. This model has been used for rapidtoxicity screening and has demonstrated in vitro-in vivo toxicityextrapolation. Hepatocyte viability was assessed microscopically bytrypan blue (0.1% w/v) exclusion test which determines plasma membranedisruption. Hepatocyte viability was determined every 30 min during the3 h incubation, and the cells were at least 80% viable before use. 800μl of each sample was added to the hepatocytes. There was nostatistically significant difference between control blank, andGd⁺³-loaded polymer and nanoparticles. The free Gd⁺³ showed significanthepatocyte toxicity, resulting in less than 15% hepatocyte survival uponexposure to 1.5 mg/ml of gadolinium solution respectively after 240minutes (FIG. 24). Exposure of hepatocytes to the same dose of Gd⁺³loaded in the polymer and nanoparticles for 240 min resulted in thesurvival of 65% and 68% for polymers and nanoparticles respectively. Thedata indicate loading Gd⁺³ to St-DTPA-PMAA-P80 polymer/nanoparticlessignificantly reduces the toxicity of the gadolinium.

Cell Viability

As a preliminary assessment of the safety of the nanoparticles for invivo use, their toxicity was assessed against free gadolinium solutionusing isolated rat hepatocytes. This model has been used for rapidtoxicity screening and has demonstrated in vitro-in vivo toxicityextrapolation. Hepatocyte viability was assessed microscopically bytrypan blue (0.1% w/v) exclusion test which determines plasma membranedisruption. Hepatocyte viability was determined every 30 min during the3 h incubation, and the cells were at least 80% viable before use. 800μl of each sample was added to the hepatocytes. There was nostatistically significant difference between control blank, andGd⁺³-loaded polymer. The free Gd⁺³ showed significant hepatocytetoxicity, resulting in less than 15% hepatocyte survival upon exposureto 1.5 mg/ml of gadolinium solution respectively after 240 minutes (FIG.25). Exposure of hepatocytes to the same dose of Gd⁺³ loaded in thepolymer and nanoparticles for 240 min resulted in the survival of 65%and 68% for polymers and nanoparticles respectively. The data indicateloading Gd⁺³ to PMAA-PS 80-g-St-DTPA polymer significantly reduces thetoxicity of the gadolinium.

Example 8 Conjugation of Near Infrared Dye (HiLyte Fluor 750) to theSt-g-PMAA-P80 Polymer and Nanoparticles

The near infrared dye (HiLyte Fluor 750) is covalently linked to theSt-g-PMAA-P80 using carbodiimide chemistry (FIG. 43A). Briefly, 20 mg ofthe polymer/nanoparticle is dispersed in DDIW water followed by additionof EDC (48 mg) and NHS (45 mg) and stirring for 90 minutes to activatethe carboxylic groups on the St-g-PMAA-P80. FIG. 43B shows the visualeffects of NIR conjugation with the nanoparticle. Subsequently, 200 μlof the Hilyte Fluor 750 hydrazide (1 mg/ml) is added and the mixture wasstirred overnight in the dark. The product is then purified by dialysisagainst water followed by freeze drying and storage at −20° C. forfuture use. The St-g-PMAA-P80 labelled with a NIR dye shows fluorescenceemission at 820 nm (FIG. 43C).

Example 9 Biodistribution and Targeting Ability of the St-g-PMAA-P80 InVivo Whole Body Fluorescence Imaging

Nanoparticles co-loaded with a NIR dye, HiLyte Fluor 750, anddoxorubicin were prepared. St-g-PMAA nanoparticles, synthesized asdescribed above and which had been freeze dried and stored in adesiccator, were used. 100 mg of the nanoparticles were dispersed in 2ml DDIW, and 30 mg of EDC/NHS were added. After 30 minutes 0.2 ml ofHilyte Fluor 750 hydrazide (1.25 mg/ml) were added while under stirring.The mixture was protected from light and stirred at room temperature for24 hrs. Finally, the product was neutralized to pH 7.4 and purified bysuccessive washing with water and centrifugation. The nanoparticles werethen loaded with Dox using the method described above.

The nanoparticle size found to be 137±3 nm with a polydispersity indexof 0.12. The diameter of these nanoparticles is thus below the pore sizeof the permeable vasculature found in many solid tumours, suggestingthat nanoparticles should be able to selectively accumulate in solidtumors by means of the enhanced permeability and retention effect (EPR).The particles were spherical and showed a porous cotton ball structure

The overall surface charge of the nanoparticles was found to be negativewith zeta potential values of −35±5. The negative surface charge can beattributed to the presence of the carboxylic acid groups and a smallamount of remnant anionic surfactant, SDS, on the surface of theparticles. The net surface charge of the nanoparticles have a pronouncedeffect on their stability as well as the adsorption of differentphysiological lipoproteins in systemic circulation and could play acritical role in the clearance of the nanoparticles in vivo. HiLyteFluor 750 content was 3.9±0.02%.

FIG. 26 shows the in vivo fluorescence images of a mouse lying on itsback. Due to very high fluorescence signal intensity of theformulations, and the near infrared emission wavelength, good tissuedepth penetration with low background interference is possible. Highlevel of fluorescence was detected 1 hr post-injection throughout thebody with the highest signal level coming from bladder indicating theexcretion of the polymer by the renal route. The detection of signalthroughout the body at early time points is possibly due to combinationof the particles being in the blood and particle deposition in skin andsubcutaneous fatty compartments. High fluorescence recorded from thehighly perfused organs, such as liver and heart could be accounted foras the combined activity of the circulating blood passing throughorgans, as well as that due to particle uptake by cells of thereticuloendothelial system (RES) recruited by the liver. The enhanceduptake in the liver is largely attributed to the macrophages residing inthese tissues, which are responsible for capturing polymers circulatingin the blood That being said compared to majority of the formulationsdiscussed in the literature, the liver uptake appears to be relativelylow. The formulation appears to be cleared from the body over time asthe fluorescence levels are almost back to the baseline after 9 days.There is only small signal detected in the liver after 9 days, and thepolymer appears to be completely eliminated from the body after 14 days.

Non-invasive real-time fluorescence imaging was utilized to track thebiodistribution and tumor accumulation of nanoparticles in Balb/c micebearing orthotopic murine EMT6 breast tumors. Owing to the near NIRemission of HiLyte Fluor™ 750 (λ_(ex)=754 nm, λ_(em)=778 nm) and thehigh fluorescence intensity of these nanoparticles, it is possible toset detection limits such that background levels of auto-fluorescencecan be reliably excluded (FIG. 26A).

FIG. 26A presents whole body images of mice at time zero (baseline) andfollowing injection of each formulation into the lateral tail vein atvarious times. At one hour post injection a clear fluorescence signal isdetectable throughout the body, due to distribution of nanoparticleswithin the blood, skin, organs and subcutaneous fat. As depicted in FIG.26A, SA-NPs and PF-NPs exhibited distinct biodistribution profiles. Onehour following injection of SA-NPs, strong fluorescence signal wasobserved in the urinary bladder (FIG. 26A, upper panels), indicatingexcretion by the renal route. The bladder signal reduced significantly 6hours post injection; however, strong fluorescence could still bedetected throughout the body suggesting both a fast and slow componentto the elimination of the SA-NPs. Importantly, mice receiving SA-NPsexhibited a strong fluorescence signal within tumor tissue, while otherperfused tissues such as the liver showed substantially lower levels ofnanoparticle accumulation. Consistent with this, inoculated tumors couldbe delineated from the surrounding histologically normal tissue,suggesting a relatively great accumulation of SA-NPs within tumors.Importantly, such fluorescence signatures persisted beyond 1 week.

A different pattern of biodistribution was observed for PF-NPs.Substantial accumulation was noted in liver and spleen at one hour postinjection, as revealed by the strong fluorescence observed in theseorgans. Moreover, these particles were not excreted efficiently via therenal route as no significant fluorescence accumulation was detectedduring the first 6 hours in the bladder. Although not studiedsystematically here, it is worth mentioning that higher levels offluorescence in fecal matter were observed in those mice injected withthe PF-NPs (personal observation), suggesting clearance of theseparticles through a hepatobiliary route largely. At one hour postinjection the tumor could be differentiated from the surrounding tissue,but the extent of PF-NP accumulation in the tumor appeared to besubstantially lower than SA-NPs.

The time-dependent excretion profiles of SA-NPs and PF-NPs were furtherquantified using the Xenogen IVIS system and plotted in FIG. 26B. SA-NPsinitially showed a rapid clearance phase, possibly due to clearancethrough urinary excretion, followed by a slower clearance at later timepoints. The average whole body NIR fluorescence intensity of SA-NPs at15 minutes post injection was 1.5±0.2×10⁸ (p/s/cm²/sr)/(μW/cm²). Itrapidly decreased to 0.87±0.05×10⁸ (p/s/cm²/sr)/(μW/cm²) by 6 hrs. Thebody fluorescence was measured to be 0.63±0.09×10⁸ (p/s/cm²/sr)/(μW/cm²)and 0.50±0.05×10⁸ (p/s/cm²/sr)/(μW/cm²) for 24 hrs and 72 hrs timepoints respectively. These values returned to baseline 14 days (336 hr)post-injection. However, the whole body fluorescence intensity of PF-NPsdecreased at much slower rate in the whole body. The body fluorescencewas measured at 1.28±0.26×10⁸ (p/s/cm²/sr)/(μW/cm²) 15 minutes postparticles administration, and slowly decreased to 0.63±0.09×10⁸(p/s/cm²/sr)/(μW/cm²) and 0.50±0.05×10⁸ (p/s/cm²/sr)/(μW/cm²) at 24 hrsand 72 hrs respectively.

The results indicate that SA-NPs undergo a fast initial elimination byexcretion through the renal route followed by a slower elimination phasewhere the particles are cleared from the body within a time span of 14days. Due to larger size and their highly cross-linked nature, thePF-NPs are not cleared by the renal route and are eliminated atsubstantially slower rate possibly via the hepatobiliary transportmechanism.

Real Time Pharmacokinetics of Nanoparticles in Tumor Tissue

The pharmacokinetic parameters for the nanoparticles in tumor wereextracted from the data in FIG. 26B and summarized in Table 6. Theseparameters pertaining to the accumulation, retention, and elimination ofnanoparticles in tumors are generally predictive of the therapeuticefficacy of nanoscale drug delivery systems. In general, the SA-NPsaccumulated to a higher degree within tumors but cleared at a fasterrate compared to that observed for PF-NPs. The peak fluorescenceintensities in the tumor were measured to be 6.15±1.04×10⁸(p/s/cm²/sr)/(μW/cm²) for SA-NPs and 0.15±0.25×10⁸ (p/s/cm²/sr)/(μW/cm²)for PF-NPs. The tumor AUC for SA-NPs was 3.5 fold larger than PF-NPsreflecting the more extensive accumulation of SA-NPs than PF-NPs in thetumor. The greater tumor accumulation of the SA-NPs is supported bytheir longer blood circulation and smaller size compared to the PF-NPs.However, PF-NPs exhibited a slower tumor clearance rate reflected by thelarge t_(1/2) value of 277±33 hrs and the smaller k_(el) of0.0025±0.0003 hrs⁻¹, while the t_(1/2) and k_(el) for the SA-NPs were92±12 hrs and 0.0075±0.0006 hrs⁻¹.

Blood Circulation and Organ Distribution of the Nanoparticles Determinedby Ex Vivo Imaging

Whole animal imaging was performed to determine tissue distribution ofthe nanoparticles (FIG. 27A). Tissue distribution and tumor accumulationwere also evaluated from ex vivo NIR fluorescence analysis of collectedblood and dissected tumors and organs, including liver, lung, kidney,spleen, skin, intestine and heart at various time points. The data arepresented as the ratio of fluorescent intensity normalized to tissueaverage baseline values (FIG. 27B,C). SA-NPs were detected at higherconcentrations and for longer time in the blood compared to the PF-NPs.Close to 30 minutes post injection, the blood fluorescent intensityratio was measured to be 150.0±12.5 and 70.0±6.0 for SA-NPs and PF-NPsrespectively. By 4 hours post-injection. these values reduced to 47±8and 4.1±0.5 respectively. Based on these data, the blood circulationhalf-life of 63 minutes and 230 minutes for PF-NPs and SA-NPs werecalculated. The PF-NPs exhibited substantially higher levels ofaccumulation in liver, spleen, lungs, heart, and intestine whilesignificantly higher levels of SA-NPs could be detected in kidney andtumor. The high level of fluorescence in the intestines of mice treatedwith PF-NPs suggests that particles accumulating in the liver areexcreted through feces. This elimination mode is generally slower thanthe elimination by urine. For this reason, fluorescence from the liverremains very strong over an extended period of time. These results arein good agreement with the whole body live animal imaging.

Microscopic Imaging of Tumor Tissue Demonstrated Extravasation of theNanoparticles in the Tumor

Tumor distribution of SA-NPs and PF-NPs at the microscopic level wasexamined using fluorescence microscopy. Tissue sections of vehicle-only(5% dextrose) infused tumors were imaged over FITC (excitation: 460-490nm, emission 500-535 nm) emission window to determine the relative levelof auto-fluorescence. As shown in FIG. 28, low levels ofauto-fluorescence were observed in some regions of vehicle-treatedtissues. Closer examination of the nature of this spectral emissiondemonstrated a broad wavelength distribution, in contrast to the moresharply defined emission peak of FITC-labeled nanoparticles. Suchauto-fluorescence arises in tissues containing lipofucin, collagen, andextended pi orbital systems such as heme. Therefore in order todefinitively distinguish auto-versus nanoparticle-mediated fluorescencewithin the FITC emission window, tissue sections were imaged over bothFITC and TRITC (excitation 540-565 nm, emission 575-620 nm) emissionwindows. Merging of these results allowed clear delineation ofauto-fluorescent (yellow green) versus nanoparticle (green) mediatedfluorescence as shown in FIG. 28. As indicated in the figure, at 4 hourspost-administration the SA-NPs accumulated to a greater extent in themouse tumor tissue compared to that seen in PF-NPs and extravasated to amuch greater extent from the tumor microvasculature into tumor-bearingtissues. In contrast, PF-NPs showed a more limited distribution withinbulk tumor parenchyma. PF-NPs were predominantly confined to largerelements of the tumor vascular and associated perivascular regions.

Example 10 In Vivo MRI Studies

The ability of the Gd⁺³-loaded PMAA-g-St-PS80 (PolyGd) and dox-loadedGd⁺³-loaded PMAA-g-St-PS80 (PolyGd-Dox) to produce positive contrastenhancement in different organs in vivo was compared to Omniscan® whichis commercially available (FIG. 21). Major organs such as liver, spleen,heart, intestine, and bladder are represented in slice A, while slice Bprovides more details on the brain, aorta, and kidneys. At the clinicaldose of 0.05 mmol/Kg Gd⁺³, Omniscan® showed minimal contrast enhancementin the liver and cardiovascular system. It was rapidly extravasated fromthe vasculature and the contrast enhancement was poor even at 5 minutespost-injection. The formulation is cleared fast from the body throughthe renal route as evident by strong bladder signal. At half theOmniscan® dose (0.025 mmol/Kg Gd⁺³), PMAA-g-St-P80 formulation producedsignificantly higher contrast in the liver, and cardiovascular system.There is a strong blood pool effect which lasts even after 60 minutesproviding evidence for the longer blood circulation half-life of thisformulation. The contrast agent appears to be eliminated by the renalroute as evident by strong contrast enhancement observed in kidneys andthen the urinary bladder. The bladder signal keeps increasing rapidlyovertime providing evidence for the excretion of the polymer through therenal route. Having a formulation which would clear through the renalroute is clinically preferable since this route of clearance is muchfaster than the hepatobiliary route.

Due to longer blood circulation of the PMAA-g-St-PS80 formulation, itssuperior contrast enhancement and blood pool effect, they could be usedin a lower total amount of Gd⁺³ and single dose instead of up to threeinjections to provide cardiac and whole body MRI scans for diagnosis andcharacterization of myocardial viability and atherosclerosis. Inaddition, with the high resolution and low dose needed to detectvasculature in detail, it is likely to provide early detection ofpathogenic conditions in highly perfused organs such as the lung, liver,kidney and microhemorrhage in the brain.

T₁-weighted images provide only a qualitative reflection of contrastagent distribution, primarily because of the sensitivity profiles of theRF transmit and receiver coils. In contrast, R₁ maps provide a betterquantitative measure of the contrast agent distribution in the wholebody.

The temporal behaviour of the whole-body distribution of contrast agentswas quantified by constructing R₁ maps at multiple time-points followinginjection without moving the animal (FIG. 27A). Organ-specificconcentration profiles were then quantified directly from R₁measurements in manually segmented regions-of-interest according toEquation 1 (described previously), (FIG. 27B,C).

The liver R₁ values increased from its baseline value of 1.0±0.1 s⁻¹ to2.1±0.3 s⁻¹ (ΔR₁˜1.1 s⁻¹) by 60 minutes post-injection, and the kidneysR₁ increased from 0.6±0.1 s⁻¹ to 1.4±0.3 s⁻¹ (ΔR₁˜0.8 s⁻¹) by 5 minutespost injection. The bladder R₁ was measured at 0.4±0.1 s⁻¹ at baseline,and increased sharply post contrast administration measuring at 1.1±0.1s⁻¹ (ΔR₁˜0.7 s⁻¹) and 2.3±0.4 s⁻¹ (ΔR₁˜1.9) by 5 minutes and 60 minutespost injection respectively. By 300 minutes, there was a significantdrop in the heart and kidney R₁ values while the liver and bladder R₁values remained high. Similar trends were observed for PolyGd-Dox. Thedata were further validated by measuring the organ Gd³⁺ content usinginductively coupled plasma atomic emission spectrography (ICP-AES) (FIG.29), and good agreement between the R₁ values and organ Gd³⁺ contentswere observed.

The R₁ of the left ventricular (LV) blood provides a useful indicator ofvascular contrast agent enhancement in whole-body images. For Omniscan®,LV R₁ increased slightly from the baseline value of 0.7±0.2 s⁻¹ to0.8±0.1 s⁻¹ (ΔR₁˜0.1 s⁻¹) by 2 minutes post injection. This increase wasnot statistically significant, and the LV R₁ values remained close tothe baseline (˜0.7 s⁻¹) at all later time points. Following PolyGdinjection, LV R₁ increased from its baseline value of 0.62±0.04 s⁻¹ to1.5±0.2 s⁻¹ (ΔR₁˜0.9 s⁻¹) by 5 minutes post-injection and remainedelevated at 1.0±0.1 s⁻¹ even after 180 minutes.

Example 11 Brain Targeting Ability of the PMAA-g-St-PS80

It has been suggested that PS80 coating of certain nanoparticles leadsto the enhanced adsorption of Apo-E from the blood to the particlesurface (FIG. 30). Subsequently, the presence of Apo-E on thenanoparticle surface promotes internalization of these nanoparticles inthe brain capillary endothelial cells via the LDL receptors expressed bythese cells. A schematic of the uptake of St-g-PMAA-P80 into themicrovessels via LDL receptors is shown in FIG. 30. TOF-SIMS is a highlysensitive, surface-specific technique enabling analysis of surfacecomposition and chemistry. Sensitivity is on the order of ppm, whilstthe surface-specificity is such that sampling is performed within thetop 1-2 nm of the specimen i.e. only the top few atomic layers aresampled. TOF-SIMS clearly shows the presence of PS 80 on the surface ofthe nanoparticles as evidenced by the characteristic peaks at 255, 265,and 283 m/z in the negative ion mode. These peaks represent the seriesof oleic and stearic fatty acids and are side chains of the sorbitanmolecule, and were absent in the control sample (no PS 80). Tof-simsdata indicating polysorbate 80 expression on the surface of theSt-g-PMAA-P80 nanoparticles are shown in FIG. 31.

To investigate the ability of the PMAA-g-St-PS80 to cross theblood-brain barrier, the MRI slices of the brain were taken. FIG. 32shows the R₁ map of the different brain slices at baseline and 20minutes after the polymer injection. Significant enhancement in brainblood vessels was observed. Also, there was significant increase in r₁values in certain areas of the brain such as sagittal sinus, ventricles,cortex and Corpus Callosum. The major enhancement in the brainventricles provides evidence for the presence of the polymer in theCerebrospinal Fluid (CSF). Examination of the R₁ map of the differentbrain slices at pre- and post-injection of nanoparticles revealedenhancement in certain brain areas such as sagittal sinus, ventricles,and to a lesser extent in cortex and sub-cortical areas. At 30 minutespost injection the R₁ values were measured at 1.1±0.1 s⁻¹, 1.1±0.1 s⁻¹,1.6±0.2 s⁻¹, and 1.7±0.1 s⁻¹ for cortex, sub-cortex, ventricles, andsagittal sinus respectively. These values decreased to 1±0.1 s⁻¹,0.9±0.1 s⁻¹, 1.5±0.3 s⁻¹, and 1.1±0.1 s⁻¹ at 180 minutes post injection(FIG. 32C).

Example 12 Ex Vivo Studies

Ex vivo studies were conducted to further confirm the brain targetingability of PMAA-g-St-PS80. The formulation was injected through tailvein and at certain time points the animals were sacrificed and thebrain was taken out, washed, and assayed for the polymer content using afluorescence technique, the blood content of the formulation was alsomeasured (FIG. 22). The presence of the fluorescence in the brain at 24hours when the blood fluorescence has returned to baseline indicates thebrain deposition of the formulations at the organ level. Moreover,fluorescence microscopy in perfused brain slices post PMAA-g-St-PS80administration was used to investigate the polymer deposition into thebrain in the cellular level (FIG. 4). Our data confirm that thePMAA-g-St-PS80 nanoparticles extravasate from the brain capillary(passing through the endothelial tight junctions) and are deposited inthe perivascular regions of the brain.

Fluorescence microscopic investigations of perfused brain tissues forformulation containing PS 80 and formulation with no PS80 wereconducted. As shown in FIG. 4B, there was no polymer-relatedfluorescence detected in perfused brain samples receiving the PMAA-g-St(no PS 80) formulation (middle panel). The PMAA-PS 80-g-St samples onthe other hand provide clear evidence of the localization ofparticle-associated fluorescence within microvessel endothelial cells aswell as in the perivascular regions of the brain capillaries (far rightpanel). There was no evidence of uptake by the neurons at the time pointstudied here (45 minutes post-injection).

Example 13 The Tumor-Targeting Potential of PMAA-g-St-PS80

The tumor targeting ability of the linear polymer was investigated usinga murine breast cancer tumor model (Balb/c mice bearing orthotopicmurine EMT6 breast tumors). The tumor accumulation was investigatedusing both in vivo fluorescence imaging and MRI (FIG. 44). The polymerexhibited excellent tumor accumulation. Tumor volume was assessed atvarious time points post treatment.

Qualitative analysis of the MIP angiograms suggested a prolonged andconstant visualization of arteries and veins after contrast mediumadministration (FIG. 36A). Quantitative analysis of individualT₁-weighted images verified a significant (P<0.05) rise in signal tonoise ratio (SNR), defined as the ratio of the inferior vena cava signalintensity divided by the standard deviation of the signal intensity andcontrast to noise ratio (CNR), defined as the difference between theinferior vena cava signal intensity and the signal intensity of thebackground soft tissue divided by the standard deviation of the signalintensity of noise, after the administration of the polymeric contrastagent, which remained elevated even 2 hrs post-injection (FIG. 36B).

FIG. 34A shows the T₁-weighted MR images and the corresponding R₁ mapsof the Balb/c mice bearing EMT6WT breast carcinoma xenografts before andat multiple time points following injection of PolyGd and PolyGd-Dox ata dose of 0.025 mmol/kg Gd³⁺. FIG. 34B displays temporal quantitative R₁changes relative to baseline (ΔR₁). A slow tumoral accumulation of themacromolecular contrast agent was observed, which was reflected by agradual increase in ΔR₁ to a peak of 0.66±0.13 s⁻¹ (PolyGd) at 2 hoursand 0.31±0.06 s⁻¹ (PolyGd-Dox) at 3 hours and then sustained AR,elevation at 0.34±0.04 s⁻¹ (PolyGd) and 0.13±0.02 s⁻¹ (PolyGd-Dox) at 48hours post injection in the tumor periphery. There was a statisticallysignificant difference between the peak ΔR₁ of PolyGd and PolyGd-Dox(p<0.05). The ability of the macromolecular contrast agents toaccumulate in the tumor is consistent with the enhanced permeation andretention effect (EPR), reflecting the prolonged blood circulation ofthe PolyGd and PolyGd-Dox coupled with the leaky nature of the tumorvasculature, and poor tumor associated lymphatic drainage.

FIG. 35 shows anti-tumor activity of starch-based nanoparticles inEMT6/WT tumor-bearing mice. Tumor cells were implanted orthotopically onday zero and mice were then treated with (A) 5% dextrose (n=2×4), (B)free Dox (n=8), PF-NPs (n=2×4), (C) PF-NPs, or (D) SA-NPs (n=2×3) at adose of 2×10 mg/kg equivalent to Dox on day 8 and 15. Tumor volume wasmeasured up to day 62. Kaplan Meier survival curves for 5% dextrose,free Dox, PF-NPs, and SA-NPs were also prepared (FIG. 35E). The trend insurvival curves was significantly different (p=0.0033, Mantel Cox)across the various treatments. Longitudinal recording of animal bodyweight was used as a general measure of animal viability, with losses of20% of total initial body weight determined as a toxic limit requiringeuthanasia. FIG. 35F shows the profiles of the body weight for micebefore and after receipt of treatment administered in FIG. 2. In noinstance did mice die or lose 20% of their body weight before tumorsreached the cut-off size of 600 mm³. All Dox groups showed some evidenceof body weight loss over the first twenty days after the start oftreatment. In general, treatment with free Dox, SA-NPs, and PF-NPsresulted in over 1 g (approximately 5%) body weight loss in only a fewmice after 30 days of the start of treatment. No changes in eating,drinking, grooming, exploratory behavior, activity, or other physicalfeatures were noted in any of the treatment groups, suggesting a lack ofgeneral toxicity due to nanoparticles at the doses administered.

The tumor fluorescence signal remained relatively strong even after 4days post injection (FIG. 44). Due to the high sensitivity of thefluorescence imaging, the tumor can be monitored for several days. TheMRI is less sensitive but provides more details on the tumor morphology,structure, and polymer distribution within the tumor. Due to thePMAA-g-St-PS80 platform to accommodate both a near infrared fluorescenceprobe and a MRI contrast agent; the two techniques can be potentiallycombined to obtain more detail information on the tumor size (e.g.,response to treatment), morphology, and polymer accumulation anddistribution in tumor overtime.

Use of doxorubicin as part of the invention is disclosed in theforegoing examples. Other drugs or therapeutics can be loaded as cargoof nanoparticles of the invention. These include, for example,amifostine, apomine, arsenic trioxide, betulinic acid, bleomycin,bortezomib, bosentan, carmustine, celecoxib, cisplatin,cyclophosphamide, cytarabine, 4-S-cysteaminyl catechol, 4-S-cysteaminylphenol, dacarbazine, docetaxel, everolimus, lenalidomide, paclitaxel,carboplatin, dacarbazine, fluorouracil, flutamide, imatinib mesylate,mercaptopurine, methotrexate, mitomycin, oxaliplatin, paclitaxel,prednisone, rituximab, sorafenib, tamoxifen, temozolomide, thalidomide,thioguanine, trastuzumab, valproic acid, vinblastine, vinblastine, etc.

The effectiveness of nanoparticles of the invention in crossing theblood brain barrier having been demonstrated, the invention includes useof nanoparticles of the invention to deliver therapeutics as loadedcargo of the nanoparticles for treatment of any of the following: aneurodegenerative disorder; a neuropsychiatric disorder; a CNS disorderselected from the group consisting of a brain tumor, epilepsy, migraine,narcolepsy, insomnia, chronic fatigue syndrome, mountain sickness,encephalitis, meningitis, and AIDS-related dementia; anangiogenesis-related disorder; an inflammatory or autoimmune disorder;age-related macular degeneration; or a lysosomal storage disease arewithin the scope of this invention. This is particularly true where theaverage size of the nanoparticles is about 100 nm or less.

Example 14 pH-Dependent Relaxivity and MR Contrast of PMAA-g-St-DTPAwith Conjugated Gd

Tumours are known to cause a decrease in local pH due to largeproduction of lactic acid from metabolism. Here we demonstratePMAA-g-St-DTPA-Gd nanoparticle could provide different relaxivity atdifferent pH values suggesting their potential use in detection of pHdeviations from normal physiological pH 7.4 in tumour tissue orinfectious lesions by MR imaging (Table 6).

Example 15 Synthesis and Characterization of Poly(DiethylaminoethylMethacrylate)-Grafted Starch (PDEAEM-g-St) and PDEAEM-g-St-DTPANanoparticles

A free-radical dispersion polymerization method was used to prepare theparticles. The polymerizations was conducted under nitrogen usingα,α′-azodiisobutyramidine dihydro-chloride (V-50) as the initiator,ethylene glycol dimethacrylate (EGDM) as the cross-linker for preformednanoparticles, and polyvinylprolidone (PVP) as the non-ionic stabilizer.The polymerization was carried out for 6 hours at 70° C. using awater-ethanol mixture (9:1). The resulting particles were washed andpurified using water and ethanol. The linear polymers of PDEAEM-g-Stwere also prepared using the same synthesis method without the use of across-linker.

The grafting of PDEAEM onto starch is confirmed with FTIR and ¹H NMRspectroscopy. TEM is used to investigate the morphology of theparticles. DLS is used to study the effect of pH and particlecomposition on size. Titration studies will be used to gain insight intothe DEAEM contents, and also the pK_(a) of the grafted copolymer.

To synthesize PDEAEM-g-St-DTPA nanoparticles, 2 g of dried starch-DTPAwas added to 40 mL of deionized water in a cleaned two-mouthed reactionflask and was left to stir until homogenous. The pH of the solution wasadjusted to approximately 8 using 0.1N NaOH solution, and was filledwith water to make up a total volume of 95 mL. The solution was placedin a heated water jacket on a stir plate, and was left to heat and stirat 70° C. while purging with nitrogen gas for 15 minutes. The initiator,V-50, was then added to the reaction flask. In a separate scintillationvial, 0.2 g PVP and water were mixed with or without 0.3-0.5 g of Tween80 and placed on a vortex apparatus until homogenous, and were thenadded to the reaction flask. In another scintillation vial, 2.0 g of themonomer, DEAEM; 754 of the crosslinker, EGDM; 5 mL ethanol and 5 mLdeionized water were added together and placed on a vortex apparatusuntil homogenous. They were then added into the reaction flask. Thereaction system was then sealed with film with loose venting, and wasleft under 70° C. for 8 hours thereafter, where it was also leftstirring overnight. Nitrogen purge was removed from the dispersion andinstead aerated the vessel. The dispersion was then transferred to a12,000-14,000 MWCO Spectra/Pore Dialysis Membrane and was left todialyze in filtered water for 24 hours, with the media being refreshedevery 2 hours, minimum 3 times. The washed sample was then dried inlight heat for another 24 hours or until crystals had formed.PDEAEM-g-St-DTPA nanoparticles and linear polymers can also be preparedby conjugating DTPA onto PDEAEM-g-St.

Stable PDEAEM-g-St latexes with solid contents of up to 4.5% weresuccessfully prepared using the described method. The dispersionpolymerization method used is fairly straight forward and does notrequire the use of oils and organic solvents making this methodadvantageous over reverse microemulsion polymerization methods.Initially, all the monomers are soluble in water, and as thepolymerization progresses the formed grafted polymer becomes insolubleat high pH and precipitate outs in form of particles, subsequently,these particles are stabilized with the aid of surfactants. Table 7summarizes the feed composition of four different batches. The graftingyield was dependent on the DEAEM concentration. Increasing the DEAEMconcentration was accompanied by increase in the grafting yield. Thiscould be explained in terms of greater availability of monomer moleculesin the proximity of starch at higher DEAEM concentrations. The starchmacroradicals are relatively immobile. As a result, the reaction ofthese macromolecules with monomers would essentially depend on theavailability of DEAEM monomers on the starch vicinity.

All nanoparticles analyzed presented a very homogeneous morphology withrelatively uniform particle size distribution and a rather sphericalshape. The nanoparticles have a smooth surface morphology. There isslight degree of particle aggregation and fusion present; however, thismight be due to nature of TEM sample preparation.

Conformation of Grafting by FTIR and ¹H NMR

The FTIR spectra of starch, PDEAEM and PDEAEM-g-St are shown in FIG. 37.In comparison with the spectrum of the native starch, the major changeis the presence of a carbonyl C═O absorption frequency at 1724 cm⁻¹ andstretch vibration of tertiary amine groups at 2962-2964 cm⁻¹. The peaksat 1166, 1090, 1020, and 954 cm⁻¹ in native starch are due to the CObond stretching. The peaks at 1090 and 1020 cm⁻¹ are characteristic ofthe anhydroglucose ring CO/CC stretching. A characteristic peak occurredat 1645 cm⁻¹ is due to the presence of bound water in starch. Abroadband due to hydrogen bonded hydroxyl group (O—H) appeared at 3450cm⁻¹ and is attributed to the complex vibrational stretching, associatedwith free, inter and intra molecular bound hydroxyl groups. The OHstretching band at 3450 cm⁻¹ is absent in the PDEAEM homopolymer. Theband at 2,916-2920 cm⁻¹ is characteristic of C—H stretching. The strongOH stretching band at 3450 cm⁻¹ in the native starch decreased inintensity following the grafting reaction implying the reaction ofstarch with DEAEM through starch OH groups. Also, the grafted polymerexhibited characteristics peaks of pyranose ring vibrations at 520-920cm⁻¹ which was absent in PDEAEM homopolymer proving the grafting ofPDEAEM onto starch.

FIG. 38 shows the ¹H-NMR spectra of a) soluble starch, c) PDEAEM, and d)PDEAEM-g-St. The starch spectrum exhibits characteristic peaks at 3.51ppm, which was attributed to CH₂ of starch units liked to C6 carbons.The peak at 3.82 ppm is attributed to the hydrogens linked to the CHunits joined to C1-C5 carbons. The peak at 5.24 ppm is attributed to thehydrogens of the R—OH hydroxyl groups. The NMR spectrum of PDEAEM-g-Stpolymer shows peaks characteristics of both starch and PDEAEM. There isa small shift in peaks at 3.34, 3.59, and 5.24 as well as a slightchange of shape in peak at 3.82 ppm due to alteration of chemicalenvironment brought on by grafting. Also, there is reduction in relativeintensity of the peak at 5.43 indicating that the starch hydroxyl groupsare participating in the grafting reaction.

Effect of pH and Starch Content on Particle Size

Dynamic light scattering was used to determine the size of thenanoparticels with various starch:DEAEM ratios in buffers of differentpH and constant ionic strength. Typical dynamic laser light scatteringdata showing the intensity weight distribution of PDEAEM-g-St particlesin PBS of pH 4 and 7.4 are shown in FIGS. 39 and 40. The particles weremonodispersed and followed a Gaussian distribution. The results in FIG.41 demonstrate that the particle size changes as the function of pH andstarch content. The PDEAEM nanoparticles had an average mean diameter of521 nm at pH 4. The size decreased to 221.8 nm at pH 7.4 due to thedeprotonation of the tertiary amine groups associated with thenanoparticles. This change in average diameter translates into 913-foldchange in volume with pH. It was observed that grafting actuallydecreased the particle size by more than two folds in some cases. Thenanoparticels with 1:1.4 molar ratio of DEAEM and starch had an averagediameter of 250 nm at low pH, and shrank to 129 nm at pH of 7.4. Ingeneral, the increase in starch content resulted in reduction in pHsensitivity. However, particles containing starch appeared to have asharper phase transition compared near the physiological pH rangecompared to PDEAEM nanoparticles.

pH-Dependent Particle Size of PDEAEM-g-St-DTPA with Loaded Gd

In a typical polymerization, the following recipe was used and Gd³⁺ wasconjugated on to the PMAA-g-St-DTPA-PS80 nanoparticles using the methodsdescribed above. The particle size in buffer solutions of various pH wasmeasured by DLS. The result in the FIG. 42 shows particle diameterincreasing as pH decreases. When the particle volume increases, theparticle hydration increases, which may generate higher relaxivity underMR and thus has the potential to image pH difference between the tumoror infectious lesion and healthy tissue. Recipe: maltodextrin-DTPA (1.4g); water (163.5 mL); NaOH added (to adjust pH, (23.5 mL to pH 8.0));ethanol (5 mL); V-50(0.2 g); PVP (0.2 g); Tween 80 (0.5 g); DEAEM (1.8g); and EGDM (65 μL).

Example 16 Delivery of Doxorubicin to Brain Tumor

A majority of therapeutic agents, including chemotherapeutic drugs (e.g.doxorubicin) and monoclonal antibodies, cannot cross the BBB and thusfail to provide effective therapy of brain tumors. As one of examples ofdelivery of therapeutic agents to brain tumors, brain metastasis ofbreast cancer was used. Ten thousand of MDA-MB231-luc 3N2 cells wereinjected intracranially.

FIG. 33A presents representative images of brain tumor acquired bybioluminescence imaging (left) and distribution of FH750-labelednanoparticles (right) injected one week post-intracranial inoculation ofthe tumor. The results strongly suggest the accumulation of thenanoparticles in the brain tumor. The images were acquired 6 hours aftertail vein injection of the nanoparticles. The fixed and sliced braintumor tissue was examined by fluorescence microscopy using an AMG EVOSflfluorescence microscope (Advanced Microscopy Group, Bothell, Wash.) andthe images were acquired using a DAPI and RFP filter set to visualizethe Hoescht33342 and NIR HF 750-labeled nanoparticles. FIG. 33B showsclearly the nanoparticles and Dox released from the nanoparticles.

Use of doxorubicin as part of the invention is disclosed in theforegoing examples. Other drugs or therapeutics can be loaded as cargoof nanoparticles of the invention. These include, for example,amifostine, apomine, arsenic trioxide, betulinic acid, bleomycin,bortezomib, bosentan, carmustine, celecoxib, cisplatin,cyclophosphamide, cytarabine, 4-S-cysteaminyl catechol, 4-S-cysteaminylphenol, dacarbazine, docetaxel, everolimus, lenalidomide, paclitaxel,carboplatin, dacarbazine, fluorouracil, flutamide, imatinib mesylate,mercaptopurine, methotrexate, mitomycin, oxaliplatin, paclitaxel,prednisone, rituximab, sorafenib, tamoxifen, temozolomide, thalidomide,thioguanine, trastuzumab, valproic acid, vinblastine, vinblastine, etc.

The effectiveness of nanoparticles of the invention in crossing theblood-brain barrier having been demonstrated, the invention includes useof nanoparticles of the invention to deliver therapeutics as loadedcargo of the nanoparticles for treatment of any of the following: aneurodegenerative disorder; a neuropsychiatric disorder; a CNS disorderselected from the group consisting of a brain tumor, epilepsy, migraine,narcolepsy, insomnia, chronic fatigue syndrome, mountain sickness,encephalitis, meningitis, and AIDS-related dementia; anangiogenesis-related disorder; an inflammatory or autoimmune disorder;age-related macular degeneration; or a lysosomal storage disease arewithin the scope of this invention. This is particularly true where theaverage size of the nanoparticles is about 100 nm or less.

It will be understood that recitations of numerical ranges by endpointsinclude all numbers subsumed within that range. Also, a recited rangehaving an endpoint within a different recited range is a disclosure ofany other range having endpoints of those recited ranges. For example,recitation of the ranges 20 to 350 and 10 to 300 is a disclosure of theranges 20 to 300 and 10 to 350.

The contents of all documents referred to herein, and also the contentsof U.S. Provisional Patent Application No. 61/605,995 to which thisapplication claims priority, are incorporated herein by reference.

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1. A method of producing a nanoparticle, the method comprising the stepsof: (a) solubilising a polymer in a liquid solution; (b) providing apolymerizable monomer comprising a carboxylic acid side group or analkylaminoalkyl ester side group; (c) graft polymerizing the monomer toform polymeric chains on the solubilised polymer, (d) providingethoxylated molecules having a functional group reactive with theforming chains, wherein: step (c) is conducted in the presence of theethoxylated molecules to covalently link the ethoxylated molecules tothe polymeric chains.
 2. The method of claim 1, wherein the liquidsolution comprises a hydroxylic solvent. 3-8. (canceled)
 9. The methodof claim 1, wherein the polymer of step (a) comprises starch. 10-16.(canceled)
 17. The method of claim 1, wherein the ethoxylated moleculesare a polyethoxylated sorbitan having a R(C9-C31)-C(O)O-group whereinthe sorbitan is linked to the second polymer through a C—C covalent bondof the R(C9-C31)-C(O)O-group during the step of polymerizing. 18-28.(canceled)
 29. A method of producing a nanoparticle for delivery of abiological agent, comprising the method of claim 17, wherein the agentis covalently linked to the polymer of step (a). 30-35. (canceled)
 36. Amethod of producing nanoparticles for delivery of a biological agent,comprising dispersing the agent and nanoparticles obtained by the methodof claim 17, in a liquid medium to incorporate the agent into thenanoparticles. 37-38. (canceled)
 39. A nanoparticle comprising: a firstpolymer; a second polymer grafted to the first polymer; and apolyethoxylated moiety covalently bound to the second polymer.
 40. Thenanoparticle of claim 39, wherein the second polymer comprisespolymerized vinyl groups having about one carboxyl group per two carbonsof the backbone of the second polymer. 41-42. (canceled)
 43. Thenanoparticle of claim 40, wherein the second polymer is poly(methacrylicacid).
 44. The nanoparticle of claim 39, wherein the polyethoxylatedmoiety is a sorbitan having a R(C9-C31)-C(O)O-group wherein the sorbitanis linked to the second polymer through a C—C covalent bond of theR-group. 45-46. (canceled)
 47. The nanoparticle of claim 44, wherein thefirst polymer comprises starch.
 48. The nanoparticle of claim 47,wherein the second polymer is crosslinked.
 49. A composition comprisinga plurality of nanoparticles of claim 48, further comprising apharmaceutically active agent.
 50. (canceled)
 51. A compositioncomprising a plurality of nanoparticles of any of claim 48, furthercomprising a signal molecule. 52-55. (canceled)
 56. The composition ofclaim 51, further comprising a pharmaceutically active agent.
 57. Ananoparticle comprising: a first polymer comprising a polysaccharide; asecond crosslinked polymer comprising poly(methacrylic acid) grafted tothe first polymer; and a polysorbate comprising a (C9-C31)R—C(O)O— groupcovalently bound to the second polymer by a C—C bond between the carbonbackbone of the second polymer and the R group.
 58. (canceled)
 59. Thenanoparticle of claim 57, wherein the polysorbate comprises the groups—O(CH₂CH₂O)_(w)—C(O)(C17)R, HO(CH₂CH₂O)_(x)—, HO(CH₂CH₂O)_(y)—,HO(CH₂CH₂O)_(z)—, wherein w+x+y+z=20.
 60. (canceled)
 61. Thenanoparticle of claim 59, wherein the first polymer comprises starch.62. The nanoparticle of claim 61, wherein the molar ratio of themonomeric unit of the polysaccharide to the monomeric methacrylate unitsof the poly(methacrylic acid) is between 0.2 and 8.0.
 63. Thenanoparticle of claim 62, wherein the molar ratio of the polysorbate andthe monomeric methacrylate units of the poly(methacrylic acid) isbetween 0.002 and 0.03.
 64. A method of producing a nanoparticle, themethod comprising the steps of: (a) solubilising a polymer in a liquidsolution; (b) providing a polymerizable monomer comprising analkylaminoalkyl ester side group or a monomer comprising a vinyl groupand one carboxyl group; (c) providing a crosslinker; and (d) graftpolymerizing the monomer to form polymeric chains on the solubilisedpolymer to form the nanoparticle. 65-68. (canceled)
 69. The method ofclaim 64, wherein the polymer of step (a) comprises starch. 70-73.(canceled)
 74. The method of claim 69, wherein the monomer isdiethylaminoethyl methacrylic acid. 75-96. (canceled)
 97. A nanoparticlecomprising: a first polymer comprising a polysaccharide; and a secondcrosslinked polymer comprising an alkylaminoalkyl ester of methacrylicacid, or a monomer comprising a vinyl group and one carboxyl group,grafted to the first polymer, wherein the second polymer is crosslinked.98. The nanoparticle of claim 97, wherein the second polymer ispolymerized diethylaminoethyl methacrylic acid.
 99. The nanoparticle ofclaim 97, wherein second polymer comprises polymerized methacrylic acid.100-110. (canceled)
 111. The method of claim 69, wherein the monomer ismethacrylic acid.